What is the second postulate of Einstein's theory of special relativity regarding the speed of light? Explain how the second postulate differs from the concept of the speed of light in classical physics.   (3 marks)

One of Einstein's postulates for special relativity is that the laws of physics are the same in all inertial frames of reference.

Which one of the following best describes a property of an inertial frame of reference?

1. It is travelling at a constant speed.
2. It is travelling at a speed much slower than \(c\).
3. Its movement is consistent with the expansion of the universe.
4. No observer in the frame can detect any acceleration of the frame.

Which one of the following is an example of an inertial frame of reference?

1. a bus travelling at constant velocity
2. an express train that is accelerating
3. a car turning a corner at a constant speed
4. a roller-coaster speeding up while heading down a slope

A passenger is playing billiards on a train that is travelling forwards on a level track. The ball takes the path shown when hit by the cue.
 

What can be inferred about the motion of the train?

1. It is turning left.
2. It is speeding up.
3. It is turning right.
4. It is slowing down.

In a thought experiment, a jet is travelling at 0.5 `c` relative to the ground, towards a train that is travelling at 0.1 `c` relative to the ground, as shown.
 

What is the speed of the light emitted from the train's headlight, as measured by a pilot in the jet?

1. 0.1 `c`
2. 0.4 `c`
3. 0.6 `c`
4. 1.0 `c`

Which of the following is an inertial frame of reference?

1. A rocket during launch
2. A train travelling at a constant velocity
3. A car turning a corner at a constant speed
4. A lift slowing down as it approaches the ground floor

A mass was hanging from the roof of a bus that was travelling forward on a horizontal road at a constant velocity.
 

The string holding the mass was cut. At the same instant, the bus driver applied the brakes, causing the bus to slow down at a rate of `3\ text{m s}^(-2)`.

To an observer outside the bus, the mass follows a parabolic trajectory.

Which statement correctly describes the resulting motion of the mass observed from within the frame of reference of the moving bus?

1. The mass travelled in a straight line vertically downwards.
2. The mass travelled in a straight line downwards and towards the front of the bus.
3. The mass travelled in a parabolic path downwards and towards the back of the bus.
4. The mass travelled in a parabolic path downwards and towards the front of the bus.

The diagram shows a simplified model of the Michelson-Morley experiment. It can be assumed that distances `L_1` and `L_2` are equal without affecting the outcome.
 

The times taken for the light to travel in both directions along the lengths `L_1` and `L_2` are `t_1` and `t_2` respectively.

What was Michelson attempting to demonstrate in this experiment?

1. The relativistic contraction of `L_1` would cause `t_1` to be less than `t_2`.
2. The ether is carried through space with Earth, which would cause `t_1` to be equal to `t_2`.
3. The times `t_1` and `t_2` would be the same because the velocity of the apparatus was much less than the speed of light.
4. The motion of the apparatus resulting from Earth's orbital motion around the sun would cause `t_1` to be greater than `t_2`.

An astronaut is travelling towards Earth in a spaceship at 0.8c. At regular intervals, a radio pulse is sent from the spaceship to an observer on Earth.

Which quantity would the astronaut and the observer measure to be the same?

1. Length of the spaceship
2. Speed of the radio pulses
3. Momentum of the astronaut
4. Time interval between the radio pulses