# AP Physics 2 : Principles of General Relativity

## Example Questions

### Example Question #1 : Principles Of General Relativity

A student on the Earth observes a spaceship moving at a considerable fraction of the speed of light. As a result of the spaceship's motion, the student observes that the clocks aboard the spaceship are running slower than when the spaceship was on the Earth. When a student aboard the spaceship observes the student's clock on the Earth, what effect will he notice on the rate of the Earth-bound clock?

Possible Answers:

The Earth-bound clock appears to run faster

The Earth-bound clock first runs slow, then fast

The Earth-bound clock appears to run slower

The Earth-bound clock first runs fast, then slow

The Earth-bound clock runs at the same rate

Correct answer:

The Earth-bound clock appears to run slower

Explanation:

For the observer on the spaceship, the Earth appears to be moving, and special relativity tells us that any observer moving at constant speed can consider him/herself stopped. Therefore, the clock on the Earth experiences the same slowing from the spaceship's viewpoint as the spaceship's clock from the Earth viewpoint. It's a little bit like looking at someone from far away. They look small due to the distance, but you do not look big to them, you also look smaller.