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Special Relativity MCQs — Physics (page 2)

90 multiple-choice questions on Special Relativity from Physics, each with the correct answer and, where available, a teacher's explanation. Read through them to revise the chapter, then practise the same questions one by one to test yourself.

26. If you could chase a light beam at 0.99c, you would measure its speed relative to you as:

  1. c
  2. 0
  3. 1.99c
  4. 0.01c

Answer: A) c

Explanation: Still c. SLO P-11-F-02 · Understanding

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27. Special relativity was published by Einstein in:

  1. 1687
  2. 1915
  3. 1955
  4. 1905

Answer: D) 1905

Explanation: His 'miracle year'. SLO P-11-F-04 · Knowledge

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28. A ball placed on the floor of a smoothly moving (constant velocity) aeroplane:

  1. rolls to the back
  2. rolls to the front
  3. rises
  4. stays at rest relative to the plane

Answer: D) stays at rest relative to the plane

Explanation: Inertial frame. SLO P-11-F-01 · Understanding

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29. A 'light clock' moving sideways ticks slower for a stationary observer because:

  1. the clock is heavier
  2. the light has to travel a longer diagonal path at the same speed c
  3. the mirrors get closer
  4. light slows down

Answer: B) the light has to travel a longer diagonal path at the same speed c

Explanation: Derivation of time dilation. SLO P-11-F-03 · Understanding

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30. A clock in a spaceship moving at 0.6c records 2 s (proper time). An Earth observer measures the interval as:

  1. 5 s
  2. 25 s
  3. 1.25 s
  4. 2.5 s

Answer: D) 2.5 s

Explanation: t = gamma t0 = 2 1 - 0.6^2 = 2.5 s. SLO P-11-F-05 · Understanding

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31. A moving rod, as measured by a stationary observer, appears:

  1. shorter along its direction of motion
  2. longer
  3. wider
  4. the same length

Answer: A) shorter along its direction of motion

Explanation: Length contraction. SLO P-11-F-03 · Understanding

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32. The speed of light in a vacuum is denoted by:

  1. c
  2. v
  3. lambda
  4. g

Answer: A) c

Explanation: From Latin 'celeritas'. SLO P-11-F-04 · Knowledge

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33. Strictly, the Earth's surface is a non-inertial frame because:

  1. it has gravity
  2. it is at rest
  3. it is very large
  4. the Earth rotates and orbits the Sun

Answer: D) the Earth rotates and orbits the Sun

Explanation: Approximately inertial for most purposes. SLO P-11-F-01 · Understanding

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34. If the laws of physics were different in different inertial frames, we could:

  1. detect absolute motion
  2. travel faster than light
  3. never move
  4. stop time

Answer: A) detect absolute motion

Explanation: First postulate forbids this. SLO P-11-F-04 · Knowledge

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35. A rod of proper length 50 m moves at 0.8c along its length. An observer at rest measures its length as:

  1. 15 m
  2. 300 m
  3. 60 m
  4. 30 m

Answer: D) 30 m

Explanation: L = L0 1 - v^2/c^2 = 50 1 - 0.8^2 = 30 m. SLO P-11-F-05 · Understanding

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36. The postulates of special relativity are supported by:

  1. no experiments
  2. experiments such as the Michelson–Morley experiment and muon decay
  3. Newton's laws
  4. only thought experiments

Answer: B) experiments such as the Michelson–Morley experiment and muon decay

Explanation: Experimental evidence. SLO P-11-F-04 · Knowledge

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37. According to the first postulate, an experiment done inside a smoothly moving closed train will:

  1. be impossible
  2. always fail
  3. give a different result
  4. give the same result as one done at rest

Answer: D) give the same result as one done at rest

Explanation: No experiment can detect uniform motion. SLO P-11-F-04 · Knowledge

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38. A lift falling freely is a frame in which objects appear:

  1. heavier
  2. to rise
  3. to fall faster
  4. weightless

Answer: D) weightless

Explanation: A freely falling frame (locally like an inertial frame without gravity). SLO P-11-F-01 · Understanding

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39. Mass–energy equivalence is expressed by:

  1. E = mc^2
  2. E = 12mv^2
  3. E = mc
  4. E = mc^2

Answer: D) E = mc^2

Explanation: Mass is a form of energy. SLO P-11-F-05 · Understanding

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40. The principle of relativity means there is no:

  1. physics law
  2. inertial frame
  3. absolute state of rest
  4. speed of light

Answer: C) absolute state of rest

Explanation: Only relative motion matters. SLO P-11-F-04 · Knowledge

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41. How many postulates does special relativity have?

  1. three
  2. one
  3. four
  4. two

Answer: D) two

Explanation: Relativity principle + constant c. SLO P-11-F-04 · Knowledge

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42. Which statement is NOT a postulate of special relativity?

  1. The speed of light is the same for all inertial observers
  2. Mass is constant at all speeds
  3. Laws of physics are the same in all inertial frames
  4. Both A and B are postulates

Answer: B) Mass is constant at all speeds

Explanation: Mass increase is a consequence. SLO P-11-F-04 · Knowledge

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43. A passenger in an accelerating bus feels pushed backward. In the bus frame, this is explained by:

  1. a real backward force from the seat
  2. air resistance
  3. gravity
  4. a fictitious force

Answer: D) a fictitious force

Explanation: The bus frame is non-inertial. SLO P-11-F-01 · Understanding

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44. The energy equivalent of 0.001 kg of mass is (c = 3 10^8 m/s):

  1. 3 10^5 J
  2. 9 10^13 J
  3. 1.8 10^14 J
  4. 4.5 10^13 J

Answer: B) 9 10^13 J

Explanation: E = mc^2 = 0.001 (3 10^8)^2 = 9 10^13 J. SLO P-11-F-05 · Understanding

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45. Clocks run slightly slower in a strong gravitational field because:

  1. air is denser
  2. light is faster
  3. space-time is curved there (gravitational time dilation)
  4. the clocks are heavier

Answer: C) space-time is curved there (gravitational time dilation)

Explanation: Confirmed by experiments and GPS. SLO P-11-F-06 · Knowledge

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46. Proper time is the time interval measured:

  1. by a moving clock
  2. by a clock at rest relative to the events
  3. on the Sun
  4. using the speed of sound

Answer: B) by a clock at rest relative to the events

Explanation: Shortest measured time interval. SLO P-11-F-03 · Understanding

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47. Planets orbit the Sun because:

  1. they are attracted magnetically
  2. they are pushed by light
  3. there is no gravity
  4. they follow the curved geometry of space-time around the Sun

Answer: D) they follow the curved geometry of space-time around the Sun

Explanation: General relativity view. SLO P-11-F-06 · Knowledge

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48. The relativity of simultaneity means that two events simultaneous for one observer:

  1. may not be simultaneous for an observer moving relative to the first
  2. never happen
  3. happen at the same place
  4. are simultaneous for everyone

Answer: A) may not be simultaneous for an observer moving relative to the first

Explanation: Simultaneity is relative. SLO P-11-F-05 · Understanding

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49. In the rubber-sheet analogy, a massive object such as the Sun:

  1. flattens space-time
  2. makes a dip (curvature) in space-time
  3. tears space-time
  4. has no effect

Answer: B) makes a dip (curvature) in space-time

Explanation: Mass curves space-time. SLO P-11-F-06 · Knowledge

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50. The effects of relativity are noticeable only when speeds are:

  1. very small
  2. close to the speed of sound
  3. zero
  4. close to the speed of light

Answer: D) close to the speed of light

Explanation: Factor gamma approx 1 at everyday speeds. SLO P-11-F-03 · Understanding

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