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Moving things around us - class-VII

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A ball lying on the ground does not move on its own because:

  1. it has inertia

  2. it has no energy

  3. it does not want to move

  4. All of the above


Correct Option: A
Explanation:

According to Newtons's first law , body remains in its state unless acted by external force. This property of body is termed as Inertia.

Option A is correct.

A tree in a park is in a state of _____with respect to the ground.

  1. rest

  2. motion

  3. data is insufficient

  4. both A and B


Correct Option: A
Explanation:

This totally depends on the frame of refrence, any object is relatively at rest or moving.

earth as  frame of refrenece in this case, the tree is at rest.

The earth is in a state of ______

  1. motion

  2. rest

  3. both a and b

  4. linear motion


Correct Option: A
Explanation:

Earth is continously moving in its orbit around the sun and on its own axis.

So, it is in the state of motion.

A book lying on a table is an example of -

  1. a body in motion

  2. a body at rest

  3. a body neither at rest nor in motion

  4. none of these


Correct Option: B
Explanation:

when the position of a body does not change with respect to its surroundings and time the body is said to be in rest. A book lying on the table is at rest because its position with respect to other object on table or room is fix. 

A book lying on a table is in a state of ____

  1. rest

  2. motion

  3. periodic motion

  4. linear motion


Correct Option: A
Explanation:

A book lying on the table is at rest. 


Since no net external force is acting on the book in this state and so it is not capable of moving the book.

Option A is correct.

Electric drill, rolling ball, wheel of a moving car, pendulum of a wall clock,spinning ball. Find the odd one out.

  1. pendulum of a wall clock

  2. Electric drill

  3. wheel of a moving car

  4. spinning ball


Correct Option: A
Explanation:

Pendulum of a wall clock- It is in periodic motion. Rest all are in multiple motion. The restoring force is proportional to displacement .While electric drill, rolling ball etc are in multiple motion like rotational +transnational or Vibrational motion.

Apple falling from a tree, car moving on a straight road, coins moving over a carrom board, giant wheel. Find the odd one out:

  1. gaint wheel

  2. Apple falling from a tree

  3.  car moving on a straight road

  4. coins moving over a carrom board


Correct Option: A
Explanation:

Giant wheel- because it has rotational motion as well as transnational motion. While apple falling from a tree, a car moving on straight rod and coin moving over a carrom board have only linear or rectilinear motion.  

Find the odd one out.
Table, chair, tree, moon

  1. moon

  2. chair 

  3. tree

  4. table


Correct Option: A
Explanation:

Moon 

When the position of a body does not change with respect its surroundings and time the body is said to be in rest.
But moon is in motion with respect to earth while other object like book ,table and tree are in rest with respect to earth . When these object are viewed from other planet ,then they will appear moving with earth velocity.  

Tree, hut, earth, dustbin, chair. Find the odd one out.

  1. earth

  2. Tree

  3. dustbin

  4. chair


Correct Option: A
Explanation:

Earth, because earth is in motion while other object are in rest with respect to earth.  

Select the odd one :

Bouncing ball, spinning top, oscillating pendulum, study table

  1. study table

  2. bouncing ball

  3. spinning top

  4. oscillating pendulum


Correct Option: A
Explanation:

All the three object are in any osscilatory motion wrt to earth as frame of refrence. But study table is at rest.

So study table is odd one out of the four objects.

Two balls of different masses have the same KE. Then the: 

  1. Heavier ball has greater momentum than the lighter ball.

  2. Lighter Will has greater momentum than the heavier ball.

  3. Both bans have equal momentum.

  4. Both balls have zero momentum.


Correct Option: A
Explanation:

The relation between kinetic energy $(K)$ and momentum $(p)$ is given by, $K=\dfrac{p^2}{2m}$ where $m$ be the mass of the body

So, $p=\sqrt{2mK}$
As kinetic energy is constant, so $p\propto \sqrt m$
Thus, the heavier ball has more momentum than that of lighter ball. 

When a body is at rest, it is obeying

  1. Principle of conservation of energy

  2. Principle of moments

  3. Newton's first law

  4. Newton's second law


Correct Option: C
Explanation:
Inertia is the tendency of an object to remain at rest or in motion. Newton's First Law of Motion states that an object will remain at rest or move at a constant speed in a straight line unless it is acted on by an unbalanced force.
So, when a body is at rest, it is obeying Newton's first law or motion or law of inertia. 

An object is said to be in motion its position (with respect to another object)

  1. changes with time

  2. does not change with time

  3. does not change

  4. is the same as before


Correct Option: A
Explanation:

Changes with time

What is corrct statement about impulse?

  1. change in velocity

  2. change in momentum due to force in small time

  3. change in acceleration

  4. change in speed


Correct Option: B
Explanation:

Impulse:- It is defined as a change in momentum due to force in small time.

Mathematically, 
From Newton's law,
$F=\dfrac{\Delta p}{\Delta t}$
Impulse, $I=F\times \Delta t=\Delta P$
The correct option is B.

A train of length 200 m traveling at $30 { ms }^{ -1 }$ overtakes another train of length 300 m traveling at $20 { ms }^{ -1 }$. The time taken by the first train to pass the second is 

  1. 10 s

  2. 30 s

  3. 40 s

  4. 50 s


Correct Option: D

 A person in a car tends to fall back when it suddenly starts. It is due to

  1. Inertia of rest

  2. Inertia of motion

  3. Inertia of direction

  4. none


Correct Option: A
Explanation:

when bus suddenly start moving in forward direction. This happens due to. When a bus suddenly starts, the standing passengers fall backward in the bus.

It is due to inertia of rest.
Hence,

option $A$ is correct answer.

The wall of your classroom is in a state of -

  1. motion

  2. rest

  3. neither rest nor motion

  4. none of these


Correct Option: B
Explanation:

The walls are at rest with respect to the Earth. When you are sitting in the classroom, you are also at rest with respect to the Earth, and so the walls do not seem to be moving to you.

If the forces acting on an object are balanced, then_____

  1. the object will be in equilibrium

  2. the object will be in motion

  3. the object will have zero acceleration

  4. the object loses its shape


Correct Option: A,C
Explanation:

according to newton's first law of motion, an object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.

so if forces acting on the object is balanced then the object will be in equilibrium and it will not have any acceleration.
cannot comment about option B because if initially object is at rest then it will be always at rest .
so best possible answer are option A,C.

If $\vec {u}=a \hat {i}+b \hat {j}+ c \hat {k}$ with $\hat {i},\hat {j},\hat {k}$ are in east, north and vertical directions, the maximum height of the projectile is ?

  1. $\dfrac{a^{2}}{2g}$

  2. $\dfrac{b^{2}}{2g}$

  3. $\dfrac{c^{2}}{2g}$

  4. $\dfrac{b^{2} c^{2}}{2g}$


Correct Option: C

The pendulum of a wall clock exhibits

  1. Rotatory motion

  2. Circular motion

  3. Linear motion

  4. Oscillatory motion


Correct Option: A

Symmetry of the laws of nature with respect to translation in time give rise to

  1. Conservation of linear momentum

  2. Conservation of angular momentum

  3. Conservation of cahrge

  4. Conservation of energy


Correct Option: A
Explanation:

Time translation symmetry gives rise to the conservation of energy.

Space translation symmetry gives rise to conservation of momentum.

Rotational symmetry gives rise to conservation of angular momentum.

The conservation law associated with this symmetry is the conservation of electrical charge.

 

A platform is moving in upward direction with uniform velocity 40 ${ ms }^{ -1 }$. When it reaches at a height of 100 m from the ground, a pocket is dropped  from it. The total distance traveled by pocket during its free fall is (Take $g=10{ ms }^{ -2 }$) 

  1. 160 m

  2. 260 m

  3. 180 m

  4. 300 m


Correct Option: C

What does the odometer of an automobile measure?

  1. Speed

  2. Distance

  3. Acceleration

  4. All


Correct Option: B
Explanation:

An odometer or odograph is an instrument that indicates distance traveled by the automobile

A laser signal sent towards the moon returns after t seconds.If c is speed of light, then the distance of the moon from the observer is

  1. ct

  2. $ct^{-1}$

  3. $ct^{-2}$

  4. $\displaystyle \frac{ct}{2}$


Correct Option: D
Explanation:

A laser signal sent towards the moon returns after t seconds.

Time taken to reach moon is $\dfrac{time}{2}=\dfrac{t}{2}$
Therefore $distance=speed*time=c*\dfrac{t}{2}$

Distance is a vector quantity. State whether true or false.

  1. True

  2. False


Correct Option: B
Explanation:

Distance is a scalar quantity. So the given statement is false.

Can a moving object cover zero distance?

  1. Always

  2. Sometimes

  3. Never

  4. Can't be said from given condition


Correct Option: C
Explanation:

A moving object always changes its position. Then, it has move along a path with some length.
So, if the body is moving, it will always cover some path which can never have zero length. Thus distance travelled by a moving object can never be zero.

Given 2x = 4, Where x is distance. Find the Value of X.

  1. 1

  2. 2

  3. 3

  4. 4


Correct Option: B
Explanation:

The given equation is  $2x  =4$

Thus  $x  = \dfrac{4}{2} = 2$

State whether given statement is True or False.
Path length is scalar Quantity ?

  1. True

  2. False


Correct Option: A
Explanation:

Path length is distance covered by body in reaching from initial point to final point. It may be different for different paths.

Since path length is distance hence it is scalar quantity, it may be different for two paths with same initial and final points.

The distance of closest approach of an $\alpha $-particle projected towards a nucleus with momentum p is r. What will be the distance of closest approach, when the momentum of projected $\alpha $-particle is 2p?

  1. 2r

  2. 4r

  3. $\dfrac { r }{ 2 } $

  4. $\dfrac { r }{ 4 } $


Correct Option: D
Explanation:

At the distance of closest approach:$KE=PE$

$\dfrac{p^2}{2m}=\dfrac{k 2 eq}{r}$
When the momentum chnages to 2p:
$\dfrac{(2p)^2}{2m}=k\dfrac{2eq}{r'}$
$\dfrac{4p^2}{2m}=k\dfrac{2eq}{r'}$
$\dfrac{2p^2}{m}=k\dfrac{2eq}{r'}$
$r'=k\dfrac{2eq}{p^2} \times \dfrac{m}{2}$
$=\dfrac{r}{2m}\times \dfrac{m}{2}$
$r'=\dfrac{r}{4}$

The height $y$ and horizontal distance $x$ covered by a projectile in a time $t$ seconds are given by the equations $y = 8t - 5t^2$ and $x = 6t$. If $x$ and $y$ are measured in meters, the velocity of projection is:-

  1. $10 \ ms^{-1}$

  2. $6 \ ms^{-1}$

  3. $8 \ ms^{-1}$

  4. $14 \ ms^{-1}$


Correct Option: A
Explanation:

$v _x=\dfrac{dx}{dt}=6$

$v _y=\dfrac{dy}{dt}=8-10t$
$\vec v=v _x\hat{i}+v _y\hat{j}$

$\vec u=\vec v _{t=0}$
$\vec u=6\hat{i}+8\hat{j}$
$u=\sqrt{6^2+8^2}$
$u=10m/s$

Estimate the force exerted by a $75 \ W$ bulb on your finger tip (are $1\ cm^{2}$), when is at a distance of $8 \ cm$ from the bulb. (Assume $100\%$ absorption)

  1. $1 \ N$

  2. $3.1 \times 10^{-10} N$

  3. $4 \times 10^{-6} N$

  4. $2 \times 10^{-4} N$


Correct Option: B
Explanation:

$\begin{array}{l} P=\frac { { \overline { S }  } }{ c } =\frac { { \frac { P }{ { 4\pi { d^{ 2 } } } }  } }{ c } =\frac { { \frac { { 75W } }{ { 4\pi { { \left( { 8.0\times { { 10 }^{ -2 } }m } \right)  }^{ 2 } } } }  } }{ { 3.00\times { { 10 }^{ 8 } }\, m/s } } =3.1\times { 10^{ -6 } }N/{ m^{ 2 } }. \ The\, \, force\, \, is\, \, pressure\, \, times\, \, area, \ we\, \, approximate\, \, the\, \, area\, \, of\, \, a\, \, fingertip\, \, to\, \, be\, \, 1.0\, c{ m^{ 2 } } \ F=PA=\left( { 3.1\times { { 10 }^{ -6 } }N/{ m^{ 2 } } } \right) \left( { 1.0\times { { 10 }^{ -4 } }{ m^{ 2 } } } \right) =3.1\times { 10^{ -10 } }N \end{array}$

Hence,
option $(B)$ is correct answer.

A boy of mass $m$ is at one end of a flat boat of mass $M$ and length $l$ which floats stationary on water. If boy moves to the other end,

  1. The boat moves in opposite direction through a distance $d = \dfrac { m l } { ( M + m ) }$

  2. The displacement of boy with respect to ground is $d ^ { 1 } = \dfrac { - M } { ( M + m ) }$

  3. The displacement of boy with reject to ground is $d^{2}=\dfrac{-M}{(M+m)}$

  4. The displacement of boy with reject to ground is$d^{3}=\dfrac{-m}{(m+M)}$


Correct Option: B

A stone is dropped under gravity from rest from a height h and it travels a distance $\frac { 9h }{ 25 } $ in the last second. What is the height 'h' ?

  1. 145 m

  2. 100 m

  3. 200m

  4. 300m


Correct Option: C

Four identical sphere each of radius $10 cm$ and mass $1 kg$ are plaed on a horizontal surface touching one another so that their centres are located at the corners of square of side $20 cm.$ What is the distance of their centre of mass from centre of either sphere$?$

  1. $5 cm$

  2. $10 cm$

  3. $20 cm$

  4. none of these


Correct Option: C

The position of a particle moving along x-axis is given as $x = 3t^2 - t^3$ , in SI units. The distance travelled by the particle in $4$ seconds, is

  1. $16\ m$

  2. $24\ m$

  3. $30\ m$

  4. $36\ m$


Correct Option: A

A boy running at an average speed of $4 km hr^{-1}$ reaches school from his home in $\frac{1}{2}hr$. The distance of the school from his home is

  1. $2 km$

  2. $8 km$

  3. $4 km$

  4. $6 km$


Correct Option: A
Explanation:

Given:$v =4\frac{Km}{h}$
           

     $t =\dfrac{1}{2}$hour
   as $v=\dfrac{Distance}{t}$
        $Distance=4\times\dfrac{1}{2}$
        $Distance=2Km$

If the displacement of an object is zero, the actual distance traversed by it will be :

  1. Zero

  2. Infinite

  3. May not be zero

  4. None of these


Correct Option: C
Explanation:

Displacement is the distance between the initial and final position of an object. When an object moves in a circular path of radius R, its displacement will be zero but the distance traveled by the object will be the perimeter i.e $2\pi R$. 

Thus, if displacement of an object is zero, the distance traversed by it may not be zero.

Sunil and Rohit start at one end of a street, the origin and run to the other end, then head back. On the way back, Sunil is ahead of Rohit. Which statement is correct about the distances run and the displacements from the origin before reaching the origin?

  1. Sunil has run a greater distance and his displacement is greater than Rohit's

  2. Rohit has run a greater distance and his displacement is greater than Sunil's

  3. Sunil has run a greater distance but his displacement is lesser that Rohit's

  4. Rohit has run a greater distance but his displacement is lesser than Sunil's


Correct Option: C
Explanation:

Before reaching origin, distance travelled by Sunil is more than Rahul since he is ahead of Rohit. But displacement of Rohit is more as he is far from the origin than Sunil.

A free falling body travels ___ of total distance in 5th second.

  1. 8 %

  2. 12 %

  3. 25 %

  4. 36 %


Correct Option: D
Explanation:
The correct option is D

Given,

A free falling body 

Distance traveled in 5s

$S=ut+\dfrac{1}{2}gt^2$ since $u=0,g=10m/s$

$=\dfrac{1}{2}\times10\times5^2$

$=12m$

Distance travelled in 5^th sis:

Distance travelled in 5s- Distance travelled in 4s

Distance travelled in $4s=\dfrac{1}{2}\times10\times4^2$

$=80m$

So,

$s _5-s _4=125-80=45$

Therefore,

$\dfrac{s _5-s _4}{s _5}\times100=\dfrac{45}{125}\times100=36\%$

A particle experiences a constant acceleration for $6s$ after starting from rest. If it travels  distance $x _{1}$ in the first two seconds and a distance $x _{2}$ in the next two next seconds and $x _{3}$in the next two seconds the n  $x _{1}: x _{2}; x _{3}::1:3:5.$

  1. True

  2. False


Correct Option: A
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