This set of Engineering Physics Multiple Choice Questions & Answers (MCQs) focuses on “Einstein’s Special Theory of Relativity”.

1. As an object approaches the speed of light, it’s mass becomes _____________

a) Zero

b) Double

c) Remains Same

d) Infinite

View Answer

Explanation: We know, for an object in motion m=\(\frac{m_0}{\sqrt{1-\frac{V^2}{c^2}}}\)

Thus, as v = c, the quantity in denominator becomes zero. Hence the mass of the object becomes infinite.

2. If the sun radiates energy at the rate of 4 x 10^{26} Js^{-1}, what is the rate at which its mass is decreasing?

a) 5.54 x 10^{9} kgs^{-1}

b) 4.44 x 10^{9} kgs^{-1}

c) 3.44 x 10^{9} kgs^{-1}

d) 2.44 x 10^{9} kgs^{-1}

View Answer

Explanation: As we know from Einstein’s mass energy relation, E = mc

^{2}.

Therefore, ΔE= Δmc

^{2}

ΔE = 4 x 10

^{26}Js

^{-1}, c = 3 x 10

^{8}ms

^{-1}.

Δm = 4 x 10

^{26}Js

^{-1}/ 9 x 10

^{16}m

^{2}s

^{-2}

Δm = 4.44 x 10

^{9}kgs

^{-1}.

3. The orbit of mercury is changing slightly due to the sun’s gravity.

a) True

b) False

View Answer

Explanation: According to Einstein’s theory of relativity, a massive object distorted space and time. Thus, due to the curvature of space-time around the massive sun, the orbit of mercury is shifting gradually over time.

4. According to Einstein’s Special Theory of Relativity, laws of physics can be formulated based on ____________

a) Inertial Frame of Reference

b) Non-Inertial Frame of Reference

c) Both Inertial and Non-Inertial Frame of Reference

d) Quantum State

View Answer

Explanation: One of the postulates of Einstein’s Special Theory of Relativity states that all the inertial frames are equivalent to the formulation of laws of physics. Thus, it is suitable for all the inertial frames.

5. For Einstein’s relation, E^{2} – p^{2}c^{2} = _____________

a) m_{o}c^{2}

b) m_{o}^{2}c^{4}

c) m_{o}c^{4}

d) m_{o}^{2}c^{6}

View Answer

Explanation: We know, E = mc

^{2}and momentum, p = mv

Now, E

^{2}– p

^{2}c

^{2}= m

^{2}c

^{4}– m

^{2}v

^{2}c

^{2}

Now, we know, m = \(\frac{m_0}{\sqrt{1-\frac{V^2}{c^2}}}\)

Therefore, E

^{2}– p

^{2}c

^{2}= m

^{2}c

^{4}(1-v

^{2}/c

^{2})

=c

^{4}m

^{2}(1-v

^{2}/c

^{2})

Using, m

^{2}(1-v2/c

^{2}) = m

_{o}

^{2}we get

E

^{2}– p

^{2}c

^{2}= m

_{o}

^{2}c

^{4}.

6. A frame of reference has four coordinates, x, y, z, and t is referred to as the_____________

a) Inertial frame of reference

b) Non-inertial frame of reference

c) Space-time reference

d) Four-dimensional plane

View Answer

Explanation: Such a frame, having four coordinates of x, y, z and time t is called the space-time frame. It plays a major role in Einstein’s special theory of relativity.

7. A man, who weighs 60 kg on earth, weighs 61 kg on a rocket, as measured by an observer on earth. What is the speed of the rocket?

a) 2.5 X 10^{8} m/s

b) 2.5 X 10^{7} m/s

c) 5.5 X 10^{7} m/s

d) 5.5 X 10^{8} m/s

View Answer

Explanation: Now, as we know m = \(\frac{m_0}{\sqrt{1-\frac{V^2}{c^2}}}\)

Here, m = 61 kg and m

_{0}= 60 kg

Therefore, 61/60 = 1/\({\sqrt{1-\frac{V^2}{c^2}}}\)

v

^{2}/c

^{2}= 1 – (60/61)

^{2}= 121/3600

v = 11 X c/60 = 5.5 X 10

^{7}m/s.

8. The momentum of a photon having energy 1.00 X 10^{-17} J is ____________

a) 2.33 X 10^{-26} kg m/s

b) 3.33 X 10^{-26} kg m/s

c) 4.33 X 10^{-26} kg m/s

d) 5.33 X 10^{-26} kg m/s

View Answer

Explanation: Now, the rest mass of a photon is zero.

Therefore, it’s momentum, p = E/c

= 1.00 X 10

^{-17}/3 X 10

^{8}

= 3.33 X 10

^{-26}kg m/s.

9. According to Einstein’s special theory of relativity, which of these objects should be the heaviest?

a) A

b) B

c) C

d) D

View Answer

Explanation: As we know, m = \(\frac{m_0}{\sqrt{1-\frac{V^2}{c^2}}}\)

Using this formula on all of the objects we get,

For object A: m = 1.127 m

_{0}

For object B: m = 2.197 m

_{0}

For object C: m = 3.034 m

_{0}

For object D: m = 0.70 m

_{0}

Hence, Object C has the highest mass.

10. Which effect is shown by the following figure?

a) Gravitational Redshift

b) Gravitational Blueshift

c) Gravitational Lensing

d) Gravitational force

View Answer

Explanation: Gravitational lensing refers to the distribution of matter between the light source and the observer such that it can bend the light coming from the source to the observer. According to Einstein’s theory of special relativity, it happens because a massive object can alter the space-time frame around itself.

**Sanfoundry Global Education & Learning Series – Engineering Physics.**

To practice all areas of Engineering Physics, __here is complete set of 1000+ Multiple Choice Questions and Answers__.