Suppose you are on board a spaceship that is passing the earth at 80% the speed of light. You see a clock on?

Question

Suppose you are on board a spaceship that is passing the earth at 80% the speed of light. You see a clock on earth tick off five seconds. How much time elapsed on your clock while this was happening?

Is it a. 5 seconds-the same as on earth's clocks b. less than 5 seconds if you are approaching earth, or more than five seconds if you are moving away c. less than 5 seconds d. more than 5 seconds

Answer 1

clock slower on the spaceship c

Answer 2

If you were standing beside the clock then you would see the hand tick off 5 seconds. If you were moving away at the speed of light you would never see the hand move because that information would never reach you (would never catch you). Therefore if you're moving away at 80% the speed of light the clock on earth will tick off less than 5 seconds in your frame of reference, or looked at the other way your clock will tick off more than 5 seconds if you're moving away from the earth. Conversely if you're approaching the earth at 80% of the speed of light you will see less than 5 seconds tick off on your clock because the information from the clock on earth is arriving faster than if you were stationary.

b) is correct.

Answer 3

b. If you're moving away from the earth at that speed, then you can only see the clock move as light reflects off it in your eyes. If you move away from it, then you are moving at about the same speed that light is trying to reach your eyes. So to you, that clock doesn't move as fast because the sight of it moving doesn't reach you as fast as the clock itself is moving. Going toward, just the opposite.

Answer 4

Just 5 seconds!

Answer 5

b.. but does that still count as doppler shift since the reference frame is the moving spaceship instead of the clock, which would time the ship's apparent movement in d-shift... or does it have another name here? ..... yeah i guess it is.....i think.