# Train, ball thrown, special relativity

#### airfrek

This is a question off a take-home exam and I just need some help getting started on each part.
1. The problem statement, all variables and given/known data
A train of length L moves at speed 3c/5 with respect to the ground. A ball is thrown from the back to the front, at speed c/3 with respect to the train. How much time does this take, and what distance does the ball cover in the train's frame, the ball's frame, and the ground's frame?

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#### nickjer

For the train and the ball's frame you can treat this as if you were stationary and threw the ball.

For the ground's frame you need to find the ball's velocity, so you use relativistic velocity addition.

You will have to show some work from here on out if you want more help :)

Last edited:

#### airfrek

Yeah I'm sorry about that. This is my first time using something like this. I wasn't sure what I was supposed to do, but yeah I'll do a better job next time. Thank you for your help.

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