• Relativistic mechanics - class-XI
Back
0

Relativistic mechanics - class-XI

Description: relativistic mechanics
Number of Questions: 20
Created by:
Tags: option a: relativity physics
Start the Quiz
Attempted 0/19 Correct 0 Score 0
‹
›

Radiation with energy that is easily detected as quanta _______________.

relativistic mechanics option a: relativity physics

  1. $1$ eV

  2. $1$ KeV

  3. $1$ MeV

  4. $10^{-10}$ eV

Show answer
Correct Option: C

Two masses of 1g and 4g are moving with equal K.E. The ratio of the magnitude of their linear momentum is-

relativistic mechanics option a: relativity physics

  1. 1 : 1

  2. 1 : 2

  3. 1 : 3

  4. 1 : 4

Show answer
Correct Option: B

Length contraction happens only __________________.

relativistic mechanics option a: relativity physics

  1. perpendicular to direction of motion

  2. along direction of motion

  3. both a and b

  4. none of these

Show answer
Correct Option: B

If a constant force acts on a particle, its acceleration will

relativistic mechanics option a: relativity physics

  1. remain constant

  2. gradually decrease

  3. gradually increase

  4. be undefined

Show answer
Correct Option: A
Explanation:
Acceleration happens because there is force applied to the object, if the force is constant, we have constant acceleration.

As the speed of a particle increases, its rest mass

relativistic mechanics option a: relativity physics

  1. increases

  2. decreases

  3. remains the same

  4. changes

Show answer
Correct Option: C
Explanation:

Rest mass $(m _o)$ is defined as the mass of the object at rest (or in rest frame) which remains constant.

Only the mass of the moving object changes as the speed increases  via   $m  = \dfrac{m _o}{\sqrt{1-\dfrac{v^2}{c^2}}}$
Hence option C is correct.

If $M$ and $m$ are moving mass and rest mass respectively of a body and $c$ is speed of light,

then kinetic energy of body is given by :

relativistic mechanics option a: relativity physics

  1. $K = [m - M]c^2$

  2. $K = [M - m]c^2$

  3. $K = Mc^2$

  4. $K = mc^2$

Show answer
Correct Option: B

A person is watching a rocket with an astronaut inside move by at a speed near the speed of light.
Which of the following statements is true?

relativistic mechanics option a: relativity physics

  1. The mass of the rocket is greater from the person's perspective than from the astronaut's perspective

  2. The mass of the rocket is the same from the perspective of the person and the astronaut

  3. The mass of the rocket is greater from the perspective of the astronaut than from the perspective of the person

  4. The person's mass is greater, from his own perspective, as the rocket flies by, than it was before the rocket flew by

  5. The astronaut's mass is greater, from his own perspective, as he flies by the person, than it was before he flew by the person

Show answer
Correct Option: A
Explanation:

Mass of the moving object as seen by the person in rest frame,  $m = \dfrac{m _o}{\sqrt{1-v^2/c^2}}$  $\implies m>m _o$

where  $m _o$ is the rest mass as seen by the astronaut in moving frame. 
Thus mass of rocket would be greater from the person's perspective than from the astronaut's perspective.

A man flies past a woman at a speed near the speed of light. What might correctly be said by whom as the man flies by? Assume that neither the man nor the woman usually travels so fast relative to other near-by objects

relativistic mechanics option a: relativity physics

  1. The man could say, "I am more massive than usual"

  2. The man could say, "Time is passing more slowly for me the usual"

  3. The woman could say to the man, "You are more massive than usual"

  4. The woman could say to the man, " You are wider than usual"

  5. The woman could say, "Time is passing more quickly for me than usual"

Show answer
Correct Option: C
Explanation:

Mass of the moving man as seen by the woman in rest frame           $m = \dfrac{m _o}{\sqrt{1-v^2/c^2}}$      $\implies m>m _o$

where  $m _o$ is the rest mass of the man. 
Thus according to the woman, the man seems to be more massive than usual.

When a rod moves at a relativistic speed v, its mass

relativistic mechanics option a: relativity physics

  1. must increase by a factor of $\gamma$

  2. may remain unchanged

  3. may increase by a factor other than $\gamma$

  4. may decrease

Show answer
Correct Option: A
Explanation:

Mass of moving object    $m  = \dfrac{m _o}{\sqrt{1 - \dfrac{v^2}{c^2}}}   = m _o \gamma$      where $m _o$ is the rest mass and  $\gamma  = \dfrac{1}{\sqrt{1- v^2/c^2}}$

Thus mass of the moving rod must increases by a factor of  $\gamma$.

By what fraction does the mass of a boy increase when he starts running at a speed of 12 km h$^{-1}$?

relativistic mechanics option a: relativity physics

  1. $11\times {10}^{-27}$

  2. $20\times {10}^{-27}$

  3. $6.17\times {10}^{-27}$

  4. $25.89\times {10}^{-27}$

Show answer
Correct Option: C
Explanation:

Given :   $v = 12$ km/h $ = 12\times \dfrac{5}{18}  =3.33$  m/s

Mass of the boy while running       $m  =\dfrac{m _o}{\sqrt{1 - (\frac{v^2}{c^2})^2}}$
$\therefore$  Fractional increase in the mass         $\dfrac{\Delta m}{m _o} = \dfrac{\dfrac{m _o}{\sqrt{1- (v/c)^2}} - m _o}{m _o}  = [1-(v/c)^2]^{-1/2} - 1$
$\implies $     $\dfrac{\Delta m}{m _o} = 1+ \dfrac{v^2}{2c^2}  -1  = \dfrac{v^2}{2c^2}$               (for $ v<< c$)

$\therefore$    $\dfrac{\Delta m}{m _o}  = \dfrac{3.33^2}{2 (3\times 10^8)^2}   =6.17\times 10^{-17}$  kg

A girl runs a $100 m$ dash. Her dad cheers for her as he watches.
According to the special theory of relativity (although the effects would be very slight) which of the following statements could be accurately stated (because of the effects of special relativity)?

relativistic mechanics option a: relativity physics

  1. After the race, the dad could say to his daughter, "You were less massive during the race than you are now"

  2. After the race, the girl could say, "My time was a little better than I expected, but the race actually was not quite $100 m$ long

  3. During the race, the girl could yell to here dad, "You are less massive now than you were before the race!"

  4. After the race, the dad could say to his daughter, "During the race, you were taller than you are now"

  5. During the race, the girl could yell to her dad, "You are shorter than you were before the race"

Show answer
Correct Option: B
Explanation:
After the race, the girl could say, "My time was a little better than I expected, but the race actually was not quite 100m long, as Einstein's theory of special relativity states that the length of objects moving at relativistic speeds undergoes a contraction along the dimension of motion.

The dynamic mass of electron having rest mass $m _0 $ and moving with speed $0.8 c $ is :

relativistic mechanics option a: relativity physics

  1. $0.6 m _0 $

  2. $0.8 m _0 $

  3. $ \dfrac{5}{3} m _{o}$

  4. $ 1.25 m _0 $

Show answer
Correct Option: C
Explanation:

Mass of the moving electron is,

$m = \dfrac{{{m _0}}}{{\sqrt {\left( {1 - \frac{{{v^2}}}{{{c^2}}}} \right)} }}$

$ = \dfrac{{{m _0}}}{{\sqrt {\left( {1 - \frac{{{{\left( {0.8c} \right)}^2}}}{{{c^2}}}} \right)} }}$

$ = \dfrac{{{m _0}}}{{\sqrt {\left( {0.36} \right)} }}$

$ = \dfrac{{{m _0}}}{{0.6}}$

$ = \dfrac{{5{m _0}}}{3}$

Thus mass of the moving electron is $\dfrac{{5{m _0}}}{3}$.

When a material particle of rest mass $'m _0'$ attains the velocity of light, its mass becomes.

relativistic mechanics option a: relativity physics

  1. $0$

  2. $2m _0$

  3. $4m _0$

  4. Infinity

Show answer
Correct Option: D
Explanation:

Rest mass of an object is the inertial mass of that object when it is at rest. The relation between object's mass and rest mass is given by:  


$m = \dfrac{m _0}{\sqrt{1- \dfrac{v^2}{c^2}}}$

where $m _0$ is rest mass, $v$ is velocity of object and $c$ is speed of light. 
Now, if some particle attains the velocity of light then according to the equation mentioned above it's mass becomes infinity. 

Statement saying that energy is radiated or absorbed in discrete packets is given by ____________.

relativistic mechanics option a: relativity physics

  1. Planck

  2. Einstein

  3. Stephen

  4. Wien

Show answer
Correct Option: A
Explanation:
According to Planck’s quantum theory, Different atoms and molecules can emit or absorb energy in discreet quantities only. 

Quantum effects are important only when observing _____________.

relativistic mechanics option a: relativity physics

  1. small objects

  2. very large objects

  3. atomic size objects

  4. all of these

Show answer
Correct Option: C
Explanation:
Quantum theory is the theoretical basis of modern physics that explains the nature and behaviour of matter and energy on the atomic and subatomic level. So quantum effect is important only when observing atomic size objects.

The velocity of a particle is dependent on the times as $\upsilon =k(t-1)$ where $k=2\ m/s^{2}$. The distance covered in first three seconds will be

relativistic mechanics option a: relativity physics

  1. $18\ m$

  2. $5\ m$

  3. $3\ m$

  4. $6\ m$

Show answer
Correct Option: A

Special theory of relativity treats problems involving :

relativistic mechanics option a: relativity physics

  1. inertial frame of reference

  2. non-inertial frame of reference

  3. non-accelerated frame of reference

  4. accelerated frame of reference

Show answer
Correct Option: A
Explanation:
Einstein’s special theory of relativity is also based on two postulates, the constancy of the speed of electromagnetic radiation and the validity of physical laws in all inertial frame of reference

Behavior of matter on atomic level cannot be explained with ____________.

relativistic mechanics option a: relativity physics

  1. modern physics

  2. classical physics

  3. relativistic mechanics

  4. atomic spectra

Show answer
Correct Option: B
Explanation:
As Classical physics is the study of motion, projectiles, pulleys, and the planets. It mainly deals with the movement of large objects through space at a relatively low slow speed. 

According to special theory of relativity which one is not an absolute quantity?

relativistic mechanics option a: relativity physics

  1. time

  2. mass

  3. height

  4. both a and b

Show answer
Correct Option: D
Explanation:
According to classical physics time and mass are not an absolute quantity
- Hide questions
ADVERTISEMENT

Find more quizzes from top tags

general knowledge
3615 Quizzes
119858 Questions
 technology
307 Quizzes
36705 Questions
 sports
963 Quizzes
19148 Questions
 history
1187 Quizzes
13475 Questions
 physics
598 Quizzes
13441 Questions
 biology
1160 Quizzes
12174 Questions
 science & technology
551 Quizzes
11015 Questions
 chemistry
490 Quizzes
9892 Questions
 maths
518 Quizzes
9324 Questions
 softskills
0 Quizzes
7131 Questions