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Momentum (p) - class-XI

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What is the momentum of an object of mass $m$, moving with a velocity $v$?

  1. $(mv)^2$

  2. $mv^2$

  3. $1/2\ mv^2$

  4. $mv$


Correct Option: D
Explanation:

Momentum of an object is defined as the product of its mass and the velocity with which the object is moving.

Let velocity of the object be  $v$ and its mass be  $m$
$\therefore \text{Momentum},\ P = mv$

A bullet of mass 40 g moving with a speed of $90 ms^{-1}$ enters a heavy wooden block and is stopped after a distance of 60 cm. The average resistance force exerted by the block on the bullet is

  1. 180 N

  2. 220 N

  3. 270 N

  4. 320 N


Correct Option: C

Momentum is a measure of 

  1. Weight

  2. Mass

  3. Quantity of motion

  4. Velocity


Correct Option: C
Explanation:

Momentum is mass* velocity.

For motion two questions are important, " How much is moving? " and "How fast is it moving?'
For change in state, inertia is necessary. Inertia is mass for translational motion. 
So, Quantity of motion is momentum.

A long-jumper runs before jumping to 

  1. Cover greater distance

  2. Maintain momentum conservation

  3. Gain energy by running

  4. Gain momentum


Correct Option: D
Explanation:

While running a long distance, jumper tries to gain more velocity that increases his momentum. When he jumps, due this momentum, his body covers longer distance.

So, Option D is correct.

Force is directly proportional to

  1. Rate of change in distance

  2. Rate of change in velocity

  3. Momentum

  4. Rate of change in momentum


Correct Option: D
Explanation:

Second law of motion yields $F = \Delta p/\Delta t$

Which has a greater momentum, an elephant at rest or an ant in motion?

  1. Elephant

  2. Ant

  3. Neither has momentum

  4. Same


Correct Option: B
Explanation:

Momentum combines both mass and velocity. Ant has a greater momentum because of it is moving. Momentum of the elephant would be zero because it is at rest.

$SI$ units of momentum is _____ 

  1. $kg\, m/s^2$

  2. $kg \,m/s$

  3. $g \,km/hr$

  4. $kg\, km/hr$


Correct Option: B
Explanation:

$SI$ unit of momentum $= (SI\, \text{unit of}\, m).(SI\,\text{ unit of}\, v) = kg \,m/s$

The SI unit of linear momentum is $kg \ m/s^{-1}$.

  1. True

  2. False


Correct Option: A
Explanation:

Momentum = mv

Unit: kg * m/ s
So, given statement is true.

If the same force is applied on two bodies of different masses for the same time, then the change produced in the momentum of the two bodies is also same .

  1. True

  2. False


Correct Option: A
Explanation:

According to Newton's second law,

F = ma = m (v - u)/ t
Ft = mv - mu = Change in momentum
Now, for two bodies, if Ft is same, change in momentum is also same.
So, given statement is true.

Momentum is a measure of quantity of motion.

  1. True

  2. False


Correct Option: A
Explanation:

For motion there are two factors, How much is moving? and how fast is moving?

According to that force changes.
So mass and velocity both are important. Hence momentum(P = mv) is quantity of motion.

If two bodies of different masses move with the same momentum, then heavier body will have greater velocity.

  1. True

  2. False


Correct Option: B
Explanation:

momentum is P = mv

so, $ p _1 = m _1 v _1 $ and $ p _2 = m _2 v _2 $
$ p _1 = p _2 $
so, $ m _1 v _1 =m _2 v _2 $
so, if $  m _1 > m _2, $ then $ v _1< v _2 $
So, given statement is false.

A car and a lorry are moving with same momentum, if same braking force is applied, then :

  1. Car comes to rest in shorter distance.

  2. Lorry comes to rest in shorter distance.

  3. Both travels same distance before coming to rest.

  4. None


Correct Option: B
Explanation:

A car and a lorry are moving with same momentum, if same breaking force is applied, then lorry comes to rest in shorter distance as it has greater mass so moves with less velocity.

To reduce the momentum of a given body to half its original value then the velocity must be __________.

  1. reduced to half

  2. reduced to one-third

  3. doubled

  4. remain same


Correct Option: A
Explanation:

P = mv

so, $ P _1 / P _2 = v _1 / v _2 $
So, if $ P _2 = 1/ 2 \space P _1$, 
then $v _2 = 1/2\space  v _1$
So option A is correct

The linear momentum of a body at rest is zero.

  1. True

  2. False


Correct Option: A
Explanation:

P= mv

if v = 0, then P = 0
So, given statement is correct.

A force acts on a body of mass 3 kg such that its velocity changes from 4 m s$^{-1}$ to 10 m s$^{-1}$. The change in momentum of the body is :

  1. 42 kg m s$^{-1}$

  2. 2 kg m s$^{-1}$

  3. 18 kg m s$^{-1}$

  4. 11 kg m s$^{-1}$


Correct Option: C
Explanation:

$\Delta p = m(v-u) = 3 (10-4)$
$=18 kg  m  s^{-1}$

Which of the following statements are true?

  1. When the mass of a body is doubled then the momentum of a body is also doubled, provided the body maintains the same velocity.

  2. We feel pain in the hand on hitting the wall, this is a consequence of Newton's third law of motion.

  3. A table cloth can be pulled from a table without dislodging the dishes. This is due to inertia of rest.

  4. Momentum is a vector quantity.


Correct Option: A,B,C,D
Explanation:

Option A is correct .

as P = mv,
So $ P \space \alpha \space m $ if v is constant.


Option B is correct.
The pain in hand is due to reaction from the wall. It will be same in magnitude as that of applied force according to Newton's third law, for every action, there is an equal and opposite reaction.


Option C is correct.
When table cloth is pulled very fast, due to inertia dishes does not change its state. 

Option 4 is correct.
P = mv
as v (velocity) is vector, momentum is also vector.

Which of the following statements are correct regarding linear momentum of a body?

  1. It is a measure of quantity of motion contained by the body.

  2. Change in momentum is the measurement of impulse.

  3. Impulse and acceleration act in same direction to the change in momentum.

  4. Incase of uniform circular motion, the linear momentum is conserved.


Correct Option: A,B
Explanation:

Momentum, P = Mv

So, it gives quantity of motion. Option A is correct.
By Newton's second law,
Ft = mv-mu, So option B is correct.
The direction of impulse can be opposite to that of change in momentum. Option C is wrong.
The Uniform circular motion is accelerated motion. So, momentum is not conserved.
Option D is wrong.
Hence, Options A and B are correct.

A force of 100 N acts on a body of mass 2 kg for 10 s. The change in momentum of the body is:

  1. 200 N-s

  2. 250 N-s

  3. 500 N-s

  4. 1000 N-s


Correct Option: D
Explanation:

$\displaystyle F = \frac{m(v-u)}{t}$


$ \displaystyle 100 = \frac{2 (v-u)}{10}$

$\Rightarrow (v-u) = 500 m  s^{-1}$

Change in momentum $=m (v-u)$

$= 2 \times (500)$

$= 1000 \ N - s$

The time, in which a force of 2 N produces a change as momentum of 0.4 kg m s$^{-1}$ in the body is :

  1. 0.2s

  2. 0.02s

  3. 0.5s

  4. 0.05s


Correct Option: A
Explanation:

$F=\displaystyle \frac{\Delta P}{t}$
$2 = \displaystyle \frac{0.4}{t} $ (or) $t = 0.2 s$

Coefficient of restitution is related to which of the follwing parameters?

  1. Linear momentum

  2. Angular momentum

  3. Kinetic energy

  4. Moment of inertia


Correct Option: C
Explanation:

The coefficient of the restriction is related to the kinetic energy.

The correct option is C.

two bodies having $K.E 4 J $ and $9 J$ have equal mass. And their momentum are $p _1$ and $p _2$ respectively then $p _1/p _2$

  1. $4:9$

  2. $9:4$

  3. $3:2$

  4. $2:3$


Correct Option: A

The changes in a momentum of a particle,when the kinetic energy is increased by 0.1% will be:-

  1. 0.05%

  2. 0.1%

  3. 1.0%

  4. 10%


Correct Option: A
Explanation:

\begin{array}{l} The\, \, kineticenergyisE=\frac { 1 }{ 2 } m{ v^{ 2 } } \ The\, \, \, momentum\, \, is\, \, p=mv \ v=\sqrt { \frac { { 2E } }{ m }  }  \ therefore, \ \Rightarrow p=mv=m\sqrt { \frac { { 2E } }{ m }  } =\sqrt { 2mE }  \ taking\, \log  s, \ \Rightarrow \log  \, p=\frac { 1 }{ 2 } \left( { \log  2+\log  m+\log  \, E } \right)  \ differentiating: \ \Rightarrow \frac { { \Delta \, p } }{ p } =\frac { 1 }{ 2 } \left( { \frac { { \Delta m } }{ m }  } \right) +\frac { 1 }{ 2 } \left( { \frac { { \Delta E } }{ E }  } \right)  \ but, \ \Rightarrow \frac { { \Delta E } }{ E } =0.1 \ so.\, therefore, \ \Rightarrow \frac { { \Delta p } }{ p } =\frac { 1 }{ 2 } \times 0.1=0.05 \ so\, the\, correct\, option\, is\, A. \end{array}

Momentum is closely related to:

  1. force

  2. impulse

  3. velocity

  4. kinetic energy


Correct Option: C
Explanation:

Momentum of an object is due to its mass and velocity. m x v = momentum. Mass remains constant for any object. The value of momentum mostly depends on the value of velocity. Thus, velocity out of the four options is closely related to momentum.

A metal ball does not rebound when struck on a wall, whereas a rubber ball of same mass when thrown with the same velocity on the wall rebounds. From this it is inferred that:

  1. change in momentum is same in both.

  2. change in momentum in rubber ball is more.

  3. change in momentum in metal ball is more.

  4. initial momentum of metal ball is more than that of rubber ball.


Correct Option: B
Explanation:

Rubber ball has got more elasticity and the change in velocity is more in case of rubber ball which proves that change in momentum of rubber ball is more.

 A cannon ball of mass $500 g$ is fired with a speed of $15 m s^{-1}$. Find its momentum.

  1. $7500 kg$ $m$ $s^{-1}$

  2. $3750 kg$ $m$ $s^{-1}$

  3. $7.5kg$ $m$ $s^{-1}$

  4. $3.75kg$ $m$ $s^{-1}$


Correct Option: C
Explanation:

$P = m\times v$


Given m = 500 gram which is also 0.5 Kg after conversion$(500/1000 = 0.5 kg);\ v= 15 \ m/sec$

$P= 0.5\times 15 = 7.5 kg m/sec$

Hence momentum is equal to $7.5 kg\ m/sec$.

The SI unit of momentum is :

  1. $kg ms^{-1}$

  2. $kg m s^{-2}$

  3. $kg m s^{2}$

  4. $kg m^{-1}s^{-1}$


Correct Option: A
Explanation:

$\because$ $p = mv$ unit of $m = kg$
unit of $v = m$$s^{-1}$ 

$\therefore$ unit of momentum 
$P = mV$ is $kg m$$s^{-1}$.
Hence option A is the correct answer.

A body of mass $60 kg$ has the momentum $3000 kg m s^{-1}$. Calculate the speed of the body.

  1. $5ms^{-1}$

  2. $0.05ms^{-1}$

  3. $50ms^{-1}$

  4. $500ms^{-1}$


Correct Option: C
Explanation:

$ P = m\times v$
$ 3000 = 60 \times v$
$ v = 50 m/sec $
Hence velocity becomes $50 m/sec $.

Two balls A and B of masses $m$ and $2m$ are in motion with velocities $2v$ and $v$ respectively. What is the ratio of their momentum ?

  1. 1:2

  2. 2:1

  3. 1:1

  4. 4:1


Correct Option: C
Explanation:

(i) Inertia depends on mass, and since the mass of the two balls are $m$ and $2m$, So the ratio of inertia of the balls $1 : 2$

(ii)Momentum , $ p = mv$
So, as per momentum equation, it depends on both mass and velocity.
So, their ratio $= m \times  2v : 2m \times  v = 1: 1$


A body of mass m moving with a velocity v is acted upon by a force. Write expression for change in momentum  when $v\rightarrow c$.

  1. $m \Delta v$

  2. $\Delta \left( mv \right)$

  3. $v \Delta\left(m \right)$

  4. $mv$


Correct Option: B
Explanation:

As we know that momentum (p) =MAASS$\times$VELOCITY(vector quantity)
hence chance in momentum($\Delta$p)=${{m} _{2}{v} _{2}}-{{m} _{1}{v} _{1}}$=$\Delta$(mv)
where ${m} _{1}$=${m} _{2}$=m
$\Delta$v=${v} _{2}-{v} _{1}$

The linear momentum of a ball of mass $50  g$ is $0.5  kg  { m  s }^{ -1 }$. Find its velocity.

  1. $0.01$ ${ m s }^{ -1 }$

  2. $1$ ${ m s }^{ -1 }$

  3. $5$ ${ m s }^{ -1 }$

  4. $10$ ${ m s }^{ -1 }$


Correct Option: D
Explanation:

We know that $ p= mv$
where $p =0.5 kg ms^{-1}$ linear momentum
$m=50g = 0.05kg$ mass, $v =$ velocity
$\therefore v = \dfrac{p}{m}$
$\Rightarrow =\dfrac{0.5}{0.05} = 10 m/s$

The unit of linear momentum is:

  1. $N$ $s$

  2. $kg$ $m$ ${ s }^{ -2 }$

  3. $N$ ${ s }^{ -1 }$

  4. $k{ g }^{ 2 }$ $m$ ${ s }^{ -1 }$


Correct Option: A
Explanation:

Linear momentum, $p=mv$
Unit of mass $=kg$
Unit of velocity $=m/s$
Hence, Unit of linear momentum $=kg m/s = kg m/s^2\times s = Ns$

A body of mass $5   kg$ is moving with velocity $2  { ms }^{ -1 }$. Calculate its linear momentum. 

  1. $2.5$ $kg$ ${ ms }^{ -1 }$

  2. $10$ $kg$ ${ ms }^{ -1 }$

  3. $5$ $kg$ ${ ms }^{ -1 }$

  4. $20$ $kg$ ${ ms }^{ -1 }$


Correct Option: B
Explanation:

We know that $ p= mv$


where $p =$ linear momentum

$m=5kg$ mass, $v =2 m/s$ velocity

$ p = 5 \times 2 = 10 kg ms^{-1}$

A body P has mass 2 m and velocity 5 v. Another body Q has mass 8 m and velocity 1.25 v. Find out the ratio of momentum of P and Q.

  1. 2:1

  2. 1:1

  3. 1:2

  4. 3:2


Correct Option: B
Explanation:

The momentum is given as $M= mv$

Where, $m= $ mass of object, 
              $v= $ velocity of object
Momentum of first object $= 2m\times 5v = 10mv$
Momentum of second object $= 8m\times 1.25v=10mv$, taking the ratio of the magnitude of momentum of Ist and IInd objects $ |p _1|:|p _2|= 1:1$
Hence, correct answer is B.

If the acceleration of an object is zero:

  1. it must be at rest

  2. it may or may not be at rest

  3. it must be moving

  4. it must be falling freely under gravity


Correct Option: B
Explanation:

From newton's  2nd law of motion, the zero acceleration implies no external force, however, the body may have uniform velocity.

Hence the body may or may not be at rest.

State whether given statement is True or False.
It's possible to have motion in the absence of a force

  1. True

  2. False


Correct Option: A
Explanation:

From newton's  IInd law of motion, the zero acceleration implies no external force, however, the body may have uniform velocity.hence the statement is true, thus correct answer is A.

Momentum of a body is defined to be the product of its mass and:

  1. speed

  2. velocity

  3. acceleration

  4. none of these


Correct Option: B
Explanation:

The momentum is given by mass times it's velocity, and it is a vector quantity with direction same as velocity. The question states momentum is mass times it's speed, which is incorrect since it gives a scalar value. Hence the statement is false and correct answer is B.

If a car and a truck are moving with same momentum, the velocity of car is ........... the velocity of truck.

  1. Greater than

  2. Lesser than

  3. Equal to

  4. might be lesser than


Correct Option: A
Explanation:

We know, p$=$mv and the mass of car is less than truck.
However momentum are same, that shows  velocity of car is greater than the velocity of truck.

State whether the given statement is true or false :

A horse continues to apply a force in order to move a cart with a constant speed.

  1. True

  2. False


Correct Option: A
Explanation:

Horse walking or running on the ground is a case of static friction. The horse moves forward but with each step it stops and then has to move again. Thus, it has to apply a constant force to keep moving.

If the ground were frictionless after the push, the horse and the cart would keep moving at the same velocity and would not be able to change the direction.

A ball rolling along a floor doesn't continue rolling indefinitely. This is because of:

  1. Friction

  2. Mass of the body

  3. earth's gravity

  4. force of attraction


Correct Option: A
Explanation:

Force of Friction
It is the force of friction which is acting upon the ball and reducing its speed and finally making it zero.

State whether given statement is True or False.
Linear momentum is always in the direction of velocity

  1. True

  2. False


Correct Option: A
Explanation:

Linear momentum is always in the direction of Velocity.
Linear momentum is a vector quantity defined as the product of an object's mass, m, and its velocity, v. Linear momentum is denoted by the letter p and is called momentum for short: Note that a body's momentum is always in the same direction as its velocity vector. .

A batsman hits back a ball straight in the direction of the bowler without changing its initial speed of $12 ms^{-1}$. If the mass of the ball is $0.15\ kg$, determine the change in momentum of the ball. (Assume linear motion of the ball)

  1. $3.6 kg m/s$

  2. $5 kg m/s$

  3. $3.5 kg m/s$

  4. $7 kg m/s$


Correct Option: A
Explanation:

The initial momentum of ball $P _1 = m\vec{v} $, after batsman hits ball and reverses its direction, momentum of ball $P _2= -m\vec{v} $
Magnitude of change in momentum $\Delta p = \left | P _2-P _1\right | =\left | - 2m \vec{v}\right | =2m \left | \vec{v}\right | $ 
from data given in question $  m=0.15 kg ;\;  \left | \vec{ v} \right |= 12m/ s$
$\Delta P=2\times 0.15\times 12= 3. 6 kg m/ s $

A loaded transport truck with a mass of 38000 kg is travelling at 1.20 m/s. What will be the velocity of a 1400 kg car if it has the same momentum?

  1. 32.57 m/s

  2. 30 m/s

  3. 15 m/s

  4. 32.67 m/s


Correct Option: A
Explanation:

Momentum of truck $ P _{truck}= m _{truck}v _{truck}$
from given data in question $ m _{truck} = 38000 \; kg;\; v _{truck}= 1.2\; m/s$
$P _{truck}= 38000\times 1.2= 45600 \; kg m/ s$
the momentum of car is equal to momentum of truck $P _{car}= m _{car}v _{car}\Rightarrow v _{car}= 45600/ 1400= 32.57 m/s$

What is the momentum of an object of mass m, moving with a velocity v?

  1. $(mv)^2$

  2. $mv^2$

  3. $\dfrac {1}{2} mv^2$

  4. $mv$


Correct Option: D
Explanation:

Momentum is  the quantity of motion of a moving body, measured as a product of its mass and velocity.


$momentum(p)=mass(m)\times velocity(v)$

An example of a force applied in the direction of motion is:

  1. Opening a door

  2. Applying brakes suddenly to a moving car

  3. A batsman hitting a cricket ball

  4. Drawing water from a well


Correct Option: C
Explanation:

While opening the door the force applied is tangential to the motion of the door.
While applying brakes the motion is on a different axis to the force applied,
When a batsman hits a ball, both the ball and the force applied are in the same direction
While drawing water from the well the motion and the force are in different directions (mostly tangential)

A force of $10 N$ acts on a body of mass $20 kg$ for $10 s$ .Change in its momentum is:

  1. $5 kg m/s$

  2. $100 kg m/s$

  3. $200 kg m/s$

  4. $1000 kg m/s$


Correct Option: B
Explanation:

$\Delta P = F\Delta t = 10 \times 10 = 100 kg m/s$

Where,
     $\Delta$ P = Change in momentum,
          F = Applied force
     $\Delta$ t  = time for which force has been applied on the body
                   
                          

The quantity that best represents the motion of a rigid body is

  1. its mass.

  2. its speed.

  3. its velocity.

  4. its linear momentum.


Correct Option: D
Explanation:

Mass of a body is the quantity of inertia possessed by it, or in simpler words, it is the measure of resistance that a body can provide to change in its motion.
Speed is the measure of how fast a body is moving.
Velocity is the measure of how fast a body is moving along with its direction.
Linear momentum is the quantity which denoted the motion of body along with its direction.

In which of the following cases the net force is not zero?

  1. A kite skillfully held stationary in the sky

  2. A ball freely falling from a height

  3. An aeroplane rising upwards at an angle of $45^{\circ}$ with the horizontal with a constant speed

  4. A cork floating on the surface of water


Correct Option: B
Explanation:

If a ball freely falling from a height the net force applied on the ball is not zero as gravity is acting on it.

A ball of mass 'm' moves normal to a wall with a velocity 'u' and rebounds with the same speed. The change in momentum of the ball during the rebounding is

  1. 2mu towards the wall

  2. 2mu away from the wall

  3. zero

  4. mu away from the wall


Correct Option: B
Explanation:

If the collision of the ball and the wall is elastic one then the change in the momentum of the ball after collision is $= mu-(-mu)=2mu$ away from the wall.

The momentum of a 10 kg body moving at 36 km/h is:

  1. 100 kg.m/s

  2. 360 kg. m/s

  3. 3.6 kg.m/s

  4. 36000 kg .m /s


Correct Option: A
Explanation:

Given :   $m = 10$ kg             $v = 36$ km/hr $ = 36\times \dfrac{5}{18}  = 10$ m/s

Momentum of the body         $P = mv  = 10\times 10  = 100$  kg.m/s

The velocity of a body of mass 20 kg increases to 400 kgm/s in 5s. If initial velocity was 10 m/s, what is the momentum before the force acts?

  1. ${200 kg. m/s ^2}$

  2. $300\  kg.m/s$

  3. $200 \ kg.m/ s$

  4. $100 \ kg. m/s$


Correct Option: C
Explanation:

Given :   $m =20$ kg        

Initial velocity of the body        $u  = 10$ m/s
Thus initial momentum of the body         $P _i = mu  =20\times 10 = 200$  kg.m/s

The combined effect of mass and velocity is taken into account by a physical quantity called :

  1. torque

  2. moment of force

  3. momentum

  4. moment of momentum


Correct Option: C
Explanation:

Mass ad velocity both are considered to be quantities which defines motion.

The combination of both is called quantity of motion.
It is momentum.
$ P = mv$

A metallic ball strikes a wall and falls down whereas a tennis ball having the same mass and velocity bounces back. The conclusion from this is that :

  1. Both suffer equal change in momentum

  2. The tennis ball suffers a greater change in momentum

  3. Metallic ball suffers a greater change in momentum

  4. The momentum of the tennis ball is less than that of the metallic ball


Correct Option: B
Explanation:

For metallic ball,

$ \triangle P _M =0-mu=-mu$
For tennis ball,
$ \triangle P _T= -mu-mu = -2mu$
$ \therefore Option\ B\ is\ correct.$ 

Momentum is defined as :

  1. weight

  2. mass

  3. mass$\times$velocity

  4. velocity


Correct Option: C
Explanation:

Momentum is product of mass and velocity.

also known as "quantity of motion"'.

A ball comes back after an elastic collision with a wall, If initial momentum of the ball is P, the impulse on the wall after the collision is :

  1. $P$

  2. $2P$

  3. $zero$

  4. $-2P$


Correct Option: B
Explanation:

Initial momentum of the ball $=P$

 Final momentum of the ball $=-P$ 
Change in momentum $=-2P$
Impulse on the wall is equal to the change in momentum imparted on the wall $=2P$

A body of mass M collides with a wall with velocity V and rebounds with the same speed. Its change in momentum is equal to :

  1. Zero

  2. MV

  3. 2MV

  4. 3MV


Correct Option: C
Explanation:

$\Delta P={ P } _{ 1 }-{ P } _{ 2 }$ $[$ change in momentum$]$

$=MV-(-MV)\ \quad \quad \quad =-2MV$
negative sign denotes direction.
Hence option C is correct.

A disc of mass 10 g is kept floating horizontally by throwing 10 marbles per second against it from below. The marbles strike the disc normally and rebound downwards with the same speed. If the mass of each marble is 5 g, the velocity with which the marbles are striking the disc is $\displaystyle \left( g=9.8{ m }/{ { s }^{ 2 } } \right) $

  1. $\displaystyle 0.98m/s$

  2. $\displaystyle 9.8m/s$

  3. $\displaystyle 1.96m/s$

  4. $\displaystyle 19.6m/s$


Correct Option: A
Explanation:
Given that:
Mass of disc,$M=10g=0.010kg$
Mass of each marble,$m=5g=0.005kg$
Suppose the number of marbles striking the disc per second=n and velocity with which marbles strike disc is v.
Then Weight of disc acting downward$=Mg$
Change in velocity of marbles when they rebound $=v-(-v)=2v$
Therefore the change in momentum of each marble when it strikes the disc=$m * 2v=2mv$
and total momentum imparted per second to the disc$=2mnv $= The force exerted by the marbles in the upward direction
The disc will remain at rest if the net force acting on it is zero provided it is initially at rest.
Therefore for the disc to remain at rest,
Weight of disc=Upward force on it
$= Mg=2mnv$
$v=\dfrac{Mg}{2mn}=\dfrac{(0.010 *9.8)}{(2*0.005*10)}$
$=0.98 m/s$

Choose the wrong statement

  1. $1 kg \ wt = 9.8 N$

  2. Momentum is a vector quantity

  3. Force is always conserved

  4. Momentum is conserved in the absence of an external force


Correct Option: C
Explanation:

Forces that do not store energy are called nonconservative or dissipative forces. Friction is a nonconservative force, and there are others. Any friction-type force, like air resistance, is a nonconservative force.

Force is always conserved is the wrong statement.

A long-jumper runs before jumping because

  1. He covers a greater distance

  2. He maintains momentum conservation

  3. He gains energy by running

  4. He gains momentum


Correct Option: D
Explanation:

to gain momentum so that the range that he jumps is long

A body of mass $5  kg$ undergoes a change in speed form $30 m/s$ to $40  {m}/{s}$. Its momentum would increase by

  1. $50 kg {m}/{s}$

  2. $75 kg {m}/{s}$

  3. $150 kg {m}/{s}$

  4. $350 kg {m}/{s}$


Correct Option: A
Explanation:

change in momentum = 5 (40 - 30) = $50kgm/s$

A number of discs, each of momentum $M  kg  {m}/{s}$ are striking a wall at the rate of $n$ discs per minute. The force associated with these discs, in newtons, would be

  1. $\displaystyle\frac{Mn}{60}$

  2. $60 Mn$

  3. $\displaystyle\frac{M}{60n}$

  4. $\displaystyle\frac{n}{60M}$


Correct Option: A
Explanation:

The force is $F=\dfrac{\Delta P}{dt}$

$momentum=M kg.m/s$
change in time=rate of dics striking wall 
$\Delta t=\dfrac{1}{n/minute}=\dfrac{60}{n}$ 
$F=\dfrac{\Delta P}{dt}=\dfrac{M}{60/n}=\dfrac{Mn}{60}N$

A body of mass $5  kg$ undergoes a change in speed from $20$ to $0.20  {m}/{s}$. The momentum of the body would

  1. Increase by $99 kg {m}/{s}$

  2. Decrease by $99 kg {m}/{s}$

  3. Increase by $101 kg {m}/{s}$

  4. Decrease by $101 kg {m}/{s}$


Correct Option: B
Explanation:

$momentum=mass*\delta v=5kg*(20-0.20)=99kgm/s$

Hence it decreases by $99kgm/s$

A body of mass $0.1 kg$ is moving with a velocity of $15  {m}/{s}$. The momentum associated with the ball will be

  1. $0.5 kg {m}/{s}$

  2. $1.5 kg {m}/{s}$

  3. $2.5 kg {m}/{s}$

  4. $3.2 N s$


Correct Option: B
Explanation:

P =mv = 0.1 x 15 $kgm/s$ = 1.5$kgm/s$

A hammer weighing $3  kg$, moving with a velocity of $10  {m}/{s}$, strikes against the head of a spike and drives it into a block of wood. If the hammer comes to rest in $0.025  s$, the impulse associated with the hammer will be

  1. $30 N s$

  2. $-30 N s$

  3. $15 N s$

  4. $-15 N s$


Correct Option: B
Explanation:

Let J be the impulse associated with the hammer

then, $\dfrac{\Delta J}{\Delta t} = ma$ and a =$\dfrac{\Delta V}{\Delta t}$

Hence, j = m$\Delta V$

j= 3(0 - 10) Ns = -30 Ns

The combined effect of mass and velocity is taken into account by a physical quantity called 

  1. Torque

  2. Moment of force

  3. Momentum

  4. Moment of momentum


Correct Option: C
Explanation:

P = mv

i.e it takes in account the factors of both m and v .

Momentum has the same units as that of 

  1. Impulse

  2. Torque

  3. Moment of momentum

  4. Couple


Correct Option: A
Explanation:

Impulse applied to an object produces an equivalent vector change in its linear momentum, also in the same direction. The SI unit of impulse is the newton second $(N⋅s)$, and the dimensionally equivalent unit of momentum is the kilogram meter per second $(kg⋅m/s).$

Newton used the phrase 'quantity of motion' for

  1. Momentum

  2. Force

  3. Acceleration due to gravity

  4. None of these


Correct Option: A
Explanation:

quantity of motion in a body, the relative amount of its motion, as measured by its momentum, varying as the product of mass and velocity.which is define as momentum.

$Mass \times velocity$ =

  1. Impulse

  2. Momentum

  3. Area

  4. Force


Correct Option: B
Explanation:

Momentum of the body is defined as the product of mass of the body and its velocity.

$\therefore$     Momentum    $\vec{P} = m\vec{v}$

Momentum is a________quantity. Fill in the blank. 

  1. scalar

  2. vector

  3. tensor

  4. none


Correct Option: B
Explanation:

As momentum of the body has both magnitude as well as direction, thus momentum is a vector quantity.
Momentum of the body       $\vec{P} = m\vec{v}$

Momentum measures the amount of:

  1. Inertia in a body

  2. Acceleration of a body

  3. Velocity of a body

  4. Motion of a body


Correct Option: D
Explanation:

Momentum is the quantity of motion of a body which is defined as the product of mass of body and its velocity.

$\therefore$ Momentum    $P = mv$

If the momentum of a flying brick is $50\ kg\ m/s$ and its mass is $10\ kg$. Calculate its velocity?

  1. $500\ m/s$

  2. $2\ m/s$

  3. $5\ m/s$

  4. None


Correct Option: C
Explanation:

Given :    $P = 50$  $kg$ $m/s$                    $m = 10$  kg

$\therefore$ Velocity of brick       $v = \dfrac{P}{m} = \dfrac{50}{10} = 5$ $m/s$  

What will be the momentum of a stone having mass of $10\ kg$ when it is thrown with a velocity of $2\ m/s$?

  1. $30\ kg\ m/s$

  2. $5\ kg\ m/s$

  3. $2.5\ kg\ m/s$

  4. $20\ kg\ m/s$


Correct Option: D
Explanation:

Given :    $m = 10$ kg                   $v =2$ m/s

Thus momentum of a stone         $P = mv = 10\times 2 =20$  $kg$ $m/s$

Calculate the momentum of a bullet of $25\ g$ when it is fired from a gun with a velocity of $100\ m/s$:

  1. $20\ kg\ m/s$

  2. $2500\ kg\ m/s$

  3. $2.5\ kg\ m/s$

  4. None


Correct Option: C
Explanation:

Given :    $m =25$ g $= 0.025$ kg                   $v =100$ m/s

Thus momentum of the bullet         $P = mv = 0.025\times 100 =2.5$  $kg$ $m/s$

When a bullet is fired from a rifle its momentum become $20\ kg\ m/s$. If the velocity of the bullet is $1000\ m/s$ what will be its mass?

  1. $30\ g$

  2. $5\ kg$

  3. $20\ g$

  4. $500\ g$


Correct Option: C
Explanation:

Given :    $P = 20$  $kg$ $m/s$                    $v = 1000$  $m/s$

$\therefore$ Mass of bullet       $m = \dfrac{P}{v} = \dfrac{20}{1000} = 0.02$ kg  $ = 20$ g

A car having mass of $1000\ kg$ is moving with a velocity of $0.5\ m/s$. What will be its momentum?

  1. $400\ kg\ m/s$

  2. $200\ kg\ m/s$

  3. $500\ kg\ m/s$

  4. $0.05\ kg\ m/s$


Correct Option: C
Explanation:

Given :    $m = 1000$ kg                   $v =0.5$ m/s

$\therefore$  Momentum of the car         $P = mv = 1000\times 0.5 =500$  $kg$ $m/s$

A stone attains a momentum of $1\ kg\ m/s$ when it flies with a velocity of $2\ m/s$, then what will be the mass of the stone?

  1. $500\ g$

  2. $2\ kg$

  3. $2\ g$

  4. None


Correct Option: A
Explanation:

Given :    $P = 1$ $kg$ $m/s$                  $v =2$ m/s

Momentum of the stone        $P = mv$
$\therefore$  Mass of stone     $m = \dfrac{P}{v} =\dfrac{1}{2} = 0.5$ kg  $=500$ g

The mass of a goods lorry is $4000\ kg$ and the mass of goods loaded on it is $20000\ kg$. If the lorry is moving with a velocity of $2\ m/s$ what will be its momentum?

  1. $48000\ kg\ m/s$

  2. $48\ kg\ m/s$

  3. $4.8\ kg\ m/s$

  4. None


Correct Option: A
Explanation:

Given :    $m _1 = 4000$ kg           $m _2  =20000$ kg             $v =2$ m/s

Total mass of the 'lorry + goods' system      $M = 4000+20000 =24000$ kg
$\therefore$ Total momentum of the system        $P = Mv = 24000\times 2 =48000$  $kg$ $m/s$

The momentum of a toy bus of $0.01\ kg$ moving with a velocity of $5\ m/s$ is:

  1. $0.005\ kg\ m/s$

  2. $0.05\ kg\ m/s$

  3. $0.005\ N\ s$

  4. $0.5\ kg\ m/s$


Correct Option: B
Explanation:

Given :   $m =0.01$ kg           $v = 5$ m/s

Momentum of the toy         $P = mv  = 0.01\times 5 = 0.05$  $kg$ $m/s$

What does the principle of conservation of linear momentum state?

  1. The linear momentum of a system cannot be changed.

  2. The linear momentum of a system cannot remain constant.

  3. The linear momentum of a system can be changed only if internal forces act.

  4. The linear momentum of a system can be changed only if external forces acts on it.


Correct Option: D
Explanation:

The principle of conservation of linear momentum states that the linear momentum of a system can be changed only if external forces acts on it.

Which of the following balls is easier to catch even though all of them are moving with the same velocity?

  1. Tennis ball

  2. Cricket ball

  3. Basket ball

  4. Both cricket and basket ball


Correct Option: A
Explanation:
Tennis ball is lighter in weight as compare to cricket ball and thus has momentum much less than the momentum of cricket ball and basket ball ( momentum is equal to mass × velocity)
body that has large momentum possesses large impact as well thus cricket ball,basket ball having more momentum than tennis ball even if they move with same velocities causes more impact on the hands of person that tends to catch it and might sometimes get hurt thus it is easy to catch a tennis ball because its momentum is less  so is its impact

A force acts on a body of mass 3 kg such that its velocity changes from 4 m $s^{-1}$ to 10 m $s^{-1}$.Calculate the change in the momentum of the body.

  1. 2 kg m $s^{-1}$

  2. 14 kg m $s^{-1}$

  3. 18 kg m $s^{-1}$

  4. 42 kg m $s^{-1}$


Correct Option: C
Explanation:

A force acts on a body of mass 3 kg such that its velocity changes from 4 m/s to 10 m/s

change in momentum 
$\Delta p=m(v _1-v _2)=3*(10-4)=18kg m/s$

State whether true or false.
If the same force is applied on two bodies of different masses for the same time, then the change produced in the momentum of the two bodies is also the same.
  1. True

  2. False


Correct Option: A
Explanation:

Let A and B be two bodies and F be the force for t time duration.

    $a _{A}=\frac{F}{M _{A}}$  ,$a _{B}=\frac{F}{M _{B}}$
$V _{A}$ (after t)$=\frac{F _{t}}{M _{A}}$
$V _{B}$ (after t)$=\frac{F _{t}}{M _{B}}$
Momentum of A $=M _{A}V _{A}=Ft$
Momentum of B $=M _{B}V _{B}=Ft$

To reduce the momentum of a given body to half its original value, its velocity must be ___________.

  1. reduced to half

  2. doubled

  3. quadrupled

  4. kept unchanged


Correct Option: A
Explanation:

The momentum of a body is given by

          $=MV$
where M is mass and V is velocity
           $P=MV$
So if M is constant and ${P}'=\frac{P}{2}$
      $\frac{P}{2}=M{V}'$
       ${V}'=\frac{V}{2}$

The momentum of a massive object at rest is

  1. Very large

  2. Very small

  3. Zero

  4. Infinity


Correct Option: C
Explanation:

Momentum is defined as the product of the body's mass and its velocity.

$p = m \times v$
Here, object is at rest. Hence, velocity, $v = 0$.
Therefore, momentum is zero.

A parachutist with total weight $75kg$ drops vertically onto a sandy ground with a speed of $2m{ s }^{ -1 }$ and comes to a halt over a distance of $0.25m$. The average force from the ground on her is close to

  1. $600N$

  2. $1200N$

  3. $1350N$

  4. $1950N$


Correct Option: A
Explanation:

Initial velocity while dropping on the ground u=2m/s.
Parachutist was brought to rest within s=0.25 m
Therefore retardation f : $u^2=2fs; \; f=\frac{u^2}{2s}=8m/s^2$
Averarage force from ground on her close is F=mf=600 N

Which of the following statements is/are correct for internal forces?

  1. They are always balanced

  2. They are never balanced

  3. They may or may not be balanced

  4. none of these


Correct Option: C
Explanation:

An internal force acting on a system may be balanced or unbalanced.

Momentum is a measure of:

  1. weight

  2. mass

  3. quantity of motion

  4. velocity


Correct Option: C
Explanation:

In order to stop a moving body we require a force and depends on the velocity as well as its mass. It was Newton in his second law who defined this new quantity as momentum.
Momentum is the product of mass and velocity of the body or in other words momentum is the measure of quantity of motion.

Momentum has the same units as that of:

  1. impulse

  2. torque

  3. moment of momentum

  4. couple


Correct Option: A
Explanation:

Momentum = mass $\times$ velocity and its unit is $Kgms^{-1}$
Impulse of the force(J) =force $\times$ time and 
$=ma \times t$
$=m\left(\dfrac{u}{t}\right) \times t$
Thus, impulse (J) is the change of momentum and its unit is $Kgms^{-1}$

A football player kicks a $0.25kg$ ball and imparts it a velocity of $10m/s$. The contact between foot and the ball is only $\cfrac{1}{50}$th of a second. The kicking force is

  1. $250N$

  2. $125N$

  3. $0N$

  4. $3.78N$


Correct Option: B
Explanation:

Force = $\dfrac{\triangle P}{\triangle t}$ (Newtons 2nd law)


$F=\dfrac{m\triangle V}{\triangle f}=\dfrac{m(V _f-V _i)}{\triangle f}$

Force, $m=0.25kg$

and $V _f=10m/s,V _i=0m/s$

$\therefore F=\dfrac{(0.25)(10-0)}{\dfrac{1}{50}}$

$F=0.25(500)$

$F=25\times 5$

$\boxed{F=125N}$

A bullet of mass $40\ g$ is fired from a gun of mass $10\ kg$. If velocity of bullet is $400\ m/s$, then the recoil velocity of the gun will be

  1. $1.6\ m/s$ in the direction of the bullet

  2. $1.6\ m/s$ opposite to the direction of the bullet

  3. $1.8\ m/s$ in the direction of the bullet

  4. $1.8\ m/s$ opposite to the direction of the bullet


Correct Option: B
Explanation:

Let velocity of gun is $v$. 

There is no external force acting, so linear momentum will conserve.
Before the firing, Linear Momentum $=0$
After the firing, Linear momentum $= 0.04 \times 400 + 10\times v$
$\Rightarrow  0.04\times 400 + 10 \times v=0$         $\Rightarrow v= -1.6 m/s$
Hence, $1.6 m/s $ opposite to the direction of the bullet.

A force of 100 dynes acts on mass of 5 gm for 10 sec. The velocity produced is:

  1. 2 cm/sec

  2. 20 cm/sec

  3. 200 cm/sec

  4. 2000 cm/sec


Correct Option: C
Explanation:

Given that,

Force $F=100\,dyn$

Mass $m=5\,g$

Time $t=10\,s$

Initial velocity $u=0$

Now, the acceleration is

  $ F=ma $

 $ a=\dfrac{F}{m} $

 $ a=\dfrac{100\times {{10}^{-5}}}{5\times {{10}^{-3}}} $

 $ a=0.20\,m/{{s}^{2}} $

Now, from equation of motion

  $ v=u+at $

 $ v=0+0.20\times 10 $

 $ v=2\,m/s $

 $ v=200\,cm/s $

Hence, the velocity produced is $200\ cm/s$

Jahnvi is walking at $1.63 m/s$. If she weighs $583 N$, what is the magnitude of her momentum?

  1. 951 kg m/s951 kg m/s

  2. $68.8 \ kg \ m/s$

  3. $137 \ kg \ m/s$

  4. $672 \ kg \ m/s$


Correct Option: A
Explanation:
$P = mv$
$ = 1.63 \times 583$
$ = 951\,kg\,m/s$
Hence, 
No any option is match so answer is $ 951\,kg\,m/s.$

The moment P (in $kg\, ms^{-1}$) of a particle is varying with time t (in second) as $p=2+3t^2$. The force acting on the particle at $t=3s$ will be 

  1. 18 N

  2. 54 N

  3. 9 N

  4. 15 N


Correct Option: A
Explanation:

Given,

$p=2+3t^2$

From Newton's second law,
$F=\dfrac{dp}{dt}$

$F=\dfrac{d(2+3t^2)}{dt}$

$F=0+6t=6t$

At $t=3s$

$F=6\times 3=18N$
The correct option is A.

A homogeneous disc of mass 2 kg and radius 15 cm is rotating about its axis (which is fixed) with an angular velocity of 4 rad/s. The linear momentum of the disc is :

  1. 1.2 kg-m/s

  2. 1.0 kg-m/s

  3. 0.6 kg-m/s

  4. None of the above


Correct Option: C
Explanation:
The formula for angular momentum is:
$L=Iw$, where is the angular velocity and $I$  is the moment of inertia.
For a disk$,$
$I = \dfrac{1}{2}M{R^2},$ where $M$ is the mass of the disk and $R$ is the radius of the disk.
For this disk, 
$I = \frac{1}{2}M{R^2} = \dfrac{1}{2}\left( 2 \right) \times {\left( {0.15} \right)^2} = 0.0225\,kg\,{m^2}$
$L = Iw = 0.0225\,kg\,{m^2} \times \left( {4\,rad/s} \right) = 0.09\,kg\,{m^2}\,rad/s$
The linear momentum is related to the the angular momentum  by the formula; $L=pr.$
We can solve for p, the linear momentum in this equation to get,
$p = \dfrac{L}{r} = \dfrac{{0.09}}{{0.15}} = 0.6kgs$
Hence,
option $(C)$ is correct answer.

Which of the following must be true for the sum of the magnitude of the momenta of the individual particles in the system?

  1. It must be zero

  2. It could be non-zero, but it must be a constant

  3. It could be non zero, and it might not be a constant

  4. It could be zero, even if the magnitude of the total momentum is not zero


Correct Option: C
Explanation:

The sum of the magnitude of the momenta of the individual particles in the system is equal to the total mass times the velocity of centre of mass.
Velocity of COM depends upon the net external force, and as nothing is given about it we can't tell anything strictly about it.
Hence 
It could be non zero, and it might not be a constant

A force of $10 \,N$ acts on a body of mass $0.5 \,kg$ for $0.25 \,sec$ starting from rest. What is its momentum now?

  1. $2.5 \,N/sec$

  2. $0.25 \,N/sec$

  3. $0.5 \,N/sec$

  4. $0.75 \,N/sec$


Correct Option: A
Explanation:

$Ft = mV _2 - mV _1 \Longrightarrow 10 \times 0.25 = P _t - P _i, P _t = 2.5$

A rocket is moving at a constant speed in space by burning its fuel and ejecting out the burnt gases through a nozzle. 

There is a change in:

  1. momentum of the rocket

  2. mass of the rocket

  3. both A & B

  4. None of the above


Correct Option: C
Explanation:

As the rocket is moving upward by ejecting gases, its mass is getting decreased gradually. As momentum is the product of the mass and velocity that is $p = m\times v$. Hence momentum decreases as mass is decreasing.

A car of mass $600 kg$ is moving with a speed of $10 m s^{-1}$ while a scooter of mass $80 kg$ is moving with a speed of $50 m s^{-1}$. Compare their momentum.

  1. $2 : 3$

  2. $1 : 2$

  3. $3 : 1$

  4. $3 : 2$


Correct Option: D
Explanation:

As we know that momentum is nothing but product of mass and velocity. Let us substitute the given values.


Given that mass of the car as 600 kg and velocity as 10 m/sec.


Hence momentum of the car is $P=600\times 10=6000 kg m/sec$.

We have mass of the scooter as 80 kg where as velocity is 50 m/sec.

Hence momentum is $P=80\times 50=4000 kg m/sec$.

Therefore, momentum are in the ratio $3:2$.

What is the value of $p _1$ and $m _2$ ?

m (kg) v (m/s) p = mv (kgm/s)
85 60 $p _1$
$m _2$ 2.5 6.25
  1. 5100, 2.5

  2. 5.1 , 2.5

  3. 2500, 5

  4. 55, 2.6


Correct Option: A
Explanation:
m (kg) v (m/s) p = mv (kgm/s)
85 60 5100
2.5 2.5 6.25

In first case:
$ m=85kg $
$v =60 m/s$
$ p =mv = 85 \times 60 = 5100\ kg m/s$
In second  case:
$ m=? $
$v =2.5 m/s$
$ p =mv = 6.25 $
$\therefore m = \dfrac{p}{v} = \dfrac{6.25}{2.5} = 2.5\ kg$

A bullet of mass $50  g$ moving with an initial velocity $100  m  {s}^{-1}$, strikes a wooden block and comes to rest after penetrating a distance $2  cm$ in it. Calculate: (i) initial momentum of the bullet, (ii) final momentum of the bullet. 

  1. $5$ $kg$ $m$ ${s}^{-1}$, $5$ $kg$ $m$ ${s}^{-1}$

  2. $5$ $kg$ $m$ ${s}^{-1}$, $0$ $kg$ $m$ ${s}^{-1}$

  3. $5$ $kg$ $m$ ${s}^{-1}$, $2.5$ $kg$ $m$ ${s}^{-1}$

  4. $2.5$ $kg$ $m$ ${s}^{-1}$, $0$ $kg$ $m$ ${s}^{-1}$


Correct Option: B
Explanation:

Mass, $m=50\ g=0.05\ kg$

Initial velocity, $u=100\ m/s$
Final velocity, $v=0$
(i) Initial momentum, $p _i=0.05 \times 100=5\ kgm/s$
(ii) Final momentum, $p _f=0.05 \times 0 = 0$

A hockey ball of mass 200 g travelling at $10\ ms^{-1}$ is struck by a hockey stick so as to return it along its original path with a velocity of $5\ ms^{-1}$. Calculate the change of momentum which occurred in the motion of the hockey ball by the force applied by the hockey stick:

  1. $-3\ Ns$

  2. $3\ Ns$

  3. $6\ Ns$

  4. $-6\ Ns$


Correct Option: A
Explanation:

Mass of ball(m)$=$200g$=$0.2kg
Initial velocity of ball(u)$=$10m${s}^{-1}$
Final velocity of ball(v)$=$5m${s}^{-1}$
Therefore, change in momentum ($\triangle$p) $=$ Final momentum - initial momentum $=m(v-u)=0.2\times(-5-10)=-3\ kgm{s}^{-1}=-3\ Ns$

The change in momentum of a vehicle weighing 2000 kg when its speed increases from 36 km/h to 72 km/h uniformly is :

  1. 15000 kg.m/s

  2. 4000 kg.m/s

  3. 20000 kg.m/s

  4. 7200 kg.m/s


Correct Option: C
Explanation:

Given :   $m = 2000$ kg            $u = 36$ km/h $ = 36 \times \dfrac{5}{18}  = 10$ m/s                $v= 72$ km/h $ = 72 \times \dfrac{5}{18}  = 20$ m/s             

Change in momentum       $\Delta P = m(v-u) = 2000\times (20-10)  =20000$  kg.m/s

A molecule of mass $m$ of an ideal gas collides with the wall of the vessel with the velocity $v$ and returns back with the same velocity. The change in the linear momentum of the molecule will be:

  1. $4mv$

  2. $8mv$

  3. $2mv$

  4. $-2mv$


Correct Option: D
Explanation:

Initial momentum  $=mv$

Final momentum  $=-mv$

Change in momentum  $=-mv-(mv)=-2mv$

A 4-kilograms ball slides over horizontal friction less surface with velocity of 1 meter per second ball strike the post and rebounds upward perpendicular to the initial direction with same speed.
Calculate the change of momentum of the ball in initial direction.

  1. -4 kg.m/s

  2. -1 kg.m/s

  3. 0 kg.m/s

  4. 1 kg.m/s

  5. 4 kg.m/s


Correct Option: A
Explanation:

Initially the velocity of the ball in horizontal direction is $1m/s$.

Finally the velocity of ball remains in vertical direction. Thus velocity in initial direction(horizontal)=$0m/s$
Thus the change in momentum=$\vec{p _2}-\vec{p _1}=m(\vec{v _2}-\vec{v _1})=4\times (0-1)kgm/s=-4kgm/s$

A cricket ball of mass 500 g is moving with speed of $36 \,km\,h^{-1}$. It is reflected back with the same speed. What is the impulse applied on it?

  1. 20 Kg m/s

  2. 10 Kg m/s

  3. 5 Kg m/s

  4. none of the above


Correct Option: B
Explanation:

Impulse $I=$ change in momentum $=mv _2-mv _1$

Here, $v _1=-v _2=36 km/h$
So, $I=(500/1000)[-36-36]=-36 kg.m/s$
The magnitude of impulse $=36 kg.m/s$

A mass of 2 kg at rest travels for 4 seconds with an acceleration of 1.5 m $s^{-2}$. Find the gain of the momentum of the body.

  1. 5 kg m $s^{-1}$

  2. 10 kg m $s^{-1}$

  3. 12 kg m $s^{-1}$

  4. 14 kg m $s^{-1}$


Correct Option: C
Explanation:

$v=u+at=1.5\times 4=6ms^{-1}$

Gain in momentum=$mv=2\times 6=12kgms^{-1}$

A force acts on a body of mass 3 kg such that its velocity changes from $4 \,m\, s^{-1}$ to $10 \,m\, s^{-1}$. The change in momentum of the body is:

  1. $42 \,kg\, m\, s^{-1}$

  2. $2 \,kg\, m\, s^{-1}$

  3. $18 \,kg\, m\, s^{-1}$

  4. $14 \,kg\, m\, s^{-1}$


Correct Option: C
Explanation:

Given, $m=3 kg$, $v _1=4 m/s$ and $v _2=10 m/s$

Change in momentum $=p _2-p _1=mv _2-mv _2=m(v _2-v _1)=3(10-4)=18 $ $kg $ $ms^{-1}$

The time, in which a force of 2 N produces a change in momentum of $0.4\, kg\, m\, s^{-1}$ in a body whose mass is 1 kg is: 

  1. 0.2 s

  2. 0.02 s

  3. 0.5 s

  4. 0.05 s


Correct Option: A
Explanation:

Impulse $I=Ft$

also $I=$change in momentum $=0.4 kg m/s$
So, $0.4=(2)t $ or $t=0.2 s$

The time, in which a force of 4 N produces a change in momentum of 0.4 kg m $s^{-1}$ in the body is:

  1. 0.1 s

  2. 0.02 s

  3. 0.5 s

  4. 0.05 s


Correct Option: A
Explanation:

Impulse $=$ change in momentum

or $Ft=0.4$
or $t=0.4/F=0.4/2=0.2$ sec

Two bodies $A$ and $B$ having mass $M$ and $m$ respectively possesses same kinetic energy. Given that $M> m$. If ${\rho} _{A}$ and ${\rho} _{B}$ be their momentum, then which of the following statements is true?

  1. ${ \rho } _{ A }={ \rho } _{ B }$

  2. ${ \rho } _{ A }> { \rho } _{ B }$

  3. ${ \rho } _{ A }< { \rho } _{ B }$

  4. It cannot be predicted


Correct Option: C
Explanation:
Two bodies A and B having mass m and M respectively possesses same Kinetic energy : 
$K _A = K _B$
In general kinetic energy, $K = \dfrac{1}{2} mv^2 = \dfrac{p^2}{2m}$ where $p$ is momentum. 
$\therefore \dfrac{\rho _A ^2}{2M} = \dfrac{\rho _B ^2}{2m}$
$ \dfrac{\rho _A ^2}{M} = \dfrac{\rho _B ^2}{m}$
But $M>m$ and therefore for above equation to be true $\rho _A ^2 < \rho _B ^2$ or $\rho _A < \rho _B $ 

For constant non zero mass, momentum versus velocity graph is a:

  1. straight line parallel to x- axis

  2. straight line parallel to y- axis

  3. straight line passing through origin

  4. straight line passing through y- axis with an intercept


Correct Option: C
Explanation:

We know that,
Momentum = mass $ \times $ velocity
So, we know that when a graph is plotted, momentum against velocity, it is a straight line passing through the origin because momentum varies linearly with respect to velocity.

A body of mass $2 kg$ is sliding with a constant velocity of $4 m/s$ on a frictionless horizontal table. The net force required to keep the body moving with the same velocity is

  1. $8 N$

  2. $0 N$

  3. $4 N$

  4. $\dfrac { 1 }{ 2 }  N$


Correct Option: B
Explanation:

According to newton's first law of motion, an object either remains at rest or continues to move at a constant velocity, unless acted upon by an external net force.
Therefore 
The force required to keep the body moving with the same velocity is zero.

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