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Galilean and Special Relativity

Question 1

What is an inertial frame of reference?

  • A) Frames of references where there is acceleration
  • B) Circular motion
  • C) Where Newton's laws of motion apply
  • D) A frame of reference that is accelerating compared to another

Answers and Explanations

Question 2

What was one of the main postulates coined by Einstein in special relativity?

  • A) The laws of physics can differ in inertial frames of references.
  • B) The speed of light can be observed moving at a different speed to \(3\cdot 10^8\,ms^{-1}\) when observed from a moving frame of reference.
  • C) The speed of light is constant in a vacuum regardless of how it is observed.
  • D) The laws of physics don't apply to light.

Answers and Explanations

Question 3

What is known as the proper time?

  • A) The time interval measured by at least 2 clocks and then averaged
  • B) The time measured by a clock moving at constant speed relative to the observer
  • C) The time measured by a clock accelerating relative to the observer
  • D) The time interval measured by a clock at the same point in space

Answers and Explanations

Question 4

Define proper length.

  • A) The difference in the positions of the ends of the object.
  • B) The difference in the positions of the ends of the object in a stationary frame of reference.
  • C) The difference in the positions of the ends of the object in an accelerating frame of reference.
  • D) The length of the rod after it has travelled 100m.

Answers and Explanations

Question 5

What is meant by spacetime?

  • A) A coordinate system where time is parallel to space coordinates.
  • B) A coordinate system where time is perpendicular to space coordinates.
  • C) The normal \(x,y,z\) coordinate system.
  • D) Velocity-time graph.

Answers and Explanations

Question 6

What is meant by the rest mass of a particle?

  • A) The mass measured when the particle is at rest.
  • B) The mass measured by an observer in the frame of reference of the particle.
  • C) The mass measured when the particle accelerates at \(9.81\;ms^{-2}\)
  • D) The mass of the particle when it is moving at constant velocity.

Answers and Explanations

Question 7

A spaceship travels at \( 0.6c \) relative to Earth. An astronaut on the spaceship measures a time interval of 2 seconds for an event. What time interval is measured by an observer on Earth?

  • A) \( 1.6 \, \text{s} \)
  • B) \( 2 \, \text{s} \)
  • C) \( 2.5 \, \text{s} \)
  • D) \( 3.2 \, \text{s} \)

Answers and Explanations

Question 8

A rod is stationary in its own rest frame with a length of \( 5.0 \, \text{m} \). An observer in a spaceship moving at \( 0.8c \) relative to the rod measures its length. What is the observed length?

  • A) \( 2.0 \, \text{m} \)
  • B) \( 3.0 \, \text{m} \)
  • C) \( 4.0 \, \text{m} \)
  • D) \( 5.0 \, \text{m} \)

Answers and Explanations

Question 9

A spaceship traveling at \( 0.9c \) relative to Earth passes by two Earth clocks located 2 light-seconds apart (as measured in the Earth frame). If the spaceship's observer sees the two Earth clocks show the same time, what is the time difference between the two clocks in the Earth frame according to the spaceship's observer?

  • A) \( 1.8 \, \text{s} \)
  • B) \( 2 \, \text{s} \)
  • C) \( 4.4 \, \text{s} \)
  • D) \( 4 \, \text{s} \)

Answers and Explanations

Question 10

A rod of rest length \( 10 \, \text{m} \) is moving at \( 0.8c \) relative to an observer. The rod travels 100 meters in the observer's frame before reversing direction and traveling back. What is the total proper time experienced by the rod during this round trip?

  • A) \( 5 \times 10^{-6} \, \text{s} \)
  • B) \( 2.5 \times 10^{-7} \, \text{s} \)
  • C) \( 5 \times 10^{-7} \, \text{s} \)
  • D) \( 5 \times 10^{-8} \, \text{s} \)

Answers and Explanations

Question 11

Two spaceships are moving towards each other. The first spaceship moves at \( 0.6c \) relative to Earth, and the second spaceship moves at \( 0.8c \) relative to Earth. What is the relative velocity of the second spaceship as seen from the first spaceship?

  • A) \( 0.96c \)
  • B) \( 1.2c \)
  • C) \( 1.4c \)
  • D) \( 0.98c \)

Answers and Explanations

Question 12

Two events occur at the same time in one frame of reference. In another frame moving at \( 0.6c \) relative to the first frame, the events are observed to occur at different times. What is the cause of this difference?

  • A) Length contraction
  • B) Time dilation
  • C) Relativistic simultaneity
  • D) Relativistic velocity addition

Answers and Explanations

Question 13

A clock is moving at \( 0.85c \) relative to an observer. The clock measures 1 hour in its rest frame. How much time will have passed on the clock, as measured by the observer, after 5 hours in the observer's frame?

  • A) 2.0 hours
  • B) 2.6 hours
  • C) 4.5 hours
  • D) 5.5 hours

Answers and Explanations

Question 14

An astronaut is traveling at a speed of \( 0.9c \) relative to Earth. If the astronaut’s clock measures 10 years during the journey, how much time will have passed on Earth during this period?

  • A) 10 years
  • B) 15 years
  • C) 20 years
  • D) 23 years

Answers and Explanations

Question 15

In a spacetime diagram, an event is represented by the coordinates \( (x, t) \). An observer in a moving reference frame measures the coordinates of the same event as \( (x', t') \), and the event occurs at the same position in the moving frame at time \( t' = 0 \).

  • A) The event is at the same position in both reference frames.
  • B) The event occurs at the same time in both reference frames.
  • C) The event occurs at different times in both reference frames.
  • D) The event occurs at the same time in the moving frame but at a different position compared to the rest frame.

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