Unit 4 topic 1: special relativity

When measured by a stationary observer, the length of a moving object is shorter than the length of the object when it is measured in its own frame of reference because

• the frame of reference of the observer is always the real frame of reference

• observations of distant events are observations of events that occurred in the past

• a clock that is moving relative to an observer will tick faster than a clock that is at rest in the observer's own frame of reference

• the speed of light in a vacuum being the same for all observers.

Calculate the velocity of a rocket journeying from Earth to a distant planet. An observer on Earth measures the journey to have taken 3 years, whereas the time taken for the journey as measured by a clock on the rocket is 1.31 years.

• 1.1 c

• 0.90 c

• 0.75 c

• 1.3 c

• proper length

• dilated length

• Lorentz factor

• relativistic length

If you travel away from a torch while travelling at 0.8 times the speed of light (0.8 c), you will measure the speed of light to be

• 0.64 c

• 0.7 c

• 1.0 c

• 0.7 c

A person opening a door onto a veranda sees lightning on a nearby hill about 2 seconds after opening the door. An observer in a passing UFO, which is travelling 0.9 c parallel to the line between, and towards, the two events will observe that:

• the person and lightning are closer together and the time between the opening of the door and the occurrence of the lightning will be less than 2 seconds

• the person and the lightning are closer together and the time between the opening of the door and the occurrence of the lightning will be greater than 2 seconds

• the person and lightning are further apart and the time between the opening of the door and the occurrence of the lightning will be less than 2 seconds

• the person and lightning are further apart and the time between the opening of the door and the occurrence of the lightning will be greater than 2 seconds

• t

There must be a difference in observed lengths in relativistic motion, based on the fact that the times measured by two persons in relative motion do differ. This difference in length is due to the difference in times and the fact that:

• they are travelling parallel to each other

• they are travelling along perpendicular paths

• they agree on relative speed

• the timing signal takes longer to reach the observer

Moving clocks are measured to run slowly because

• the relativistic time-interval is greater than the proper time-interval

• the relativistic time-interval is greater than the proper time-interval which is measured by the moving clock

• the relativistic time-interval is greater than the proper time-interval, which is measured by the moving clock, and both clocks are describing time with a unit of the same length

• all of the above

For the two events with a time interval measured by a clock, the proper time-interval is that measured by a clock, that is

• Local to the event

• the events were at rest relative to that clock

• the start and finish occur in the same place in space relative to the position of the clock

• all of the above

Select the option that contains deduction(s) from the two postulates that are the basis of special relativity about frames of reference

• one cannot know one's constant speed with regard only to one's own frame of reference

• Simultaneity is the same in all inertial frames of reference, so the relationship between two events is that they occur at the same time in all inertial frames of reference

• the relation between two events is assumed to happen at the same time in all inertial frames of reference so the laws of physics are not the same in all inertial frames of reference

• the relation between two events is assumed to happen at the same time in all inertial frames of reference and the speed of light in a vacuum has the same value in all