00:01
Okay, so let's say your friend is on a spacecraft that is moving past to you at a speed of 0 .77 times the speed of light.
00:11
And in your frame, you measure it to have a length of, let's see, 4 .8 meters and a height of, actually i think this is just 0 .7 times the speed of light.
00:26
And a height will call this h of 1 .6 meters.
00:31
And so we want to know what is the rest link that's called this l .9.
00:36
Well, this is going to be basically the lorenz factor times the measured length that you have.
00:41
So it'll be 4 .8 meters divided by the square root of 1 minus the speed of the ship squared divided by the speed of light squared.
00:50
So 0 .7 squared.
00:57
And so if we do all that, we should get a rest length.
00:59
Length of about 6 .72 meters.
01:03
Part b asks how many seconds elapsed on your friend's watch when 23 seconds passed on yours.
01:11
So your time is related to your friend's time by a very similar relationship...