Question

You are down at the railyard at 4:30 AM to watch a taping of an Alias episode. You watch as a train goes by at 5.0 m/s south. On top of the train, Agent Sydney Bristow is running north. You see Sydney moving at 8.0 m/s North. At what speed does the camera crew on the train see Sydney running, and in what direction?

Answer 1

The speed is 13 m/s

Step-by-step explanation:

In this problem, we have two reference frames:

- The reference frame of the observer on the ground, O

- The reference frame of the observes on the train, O', moving with velocity
`v' = -5.0 m/s` with respect to O (here we have taken north as positive direction, so since the train is moving south, we wrote it as a negative number)

For the observer on the ground, O, Sydney is moving with velocity

`v = +8.0 m/s` (positive because it's moving north)

So, we can find Sydney's velocity with respect to the frame O' as follows

`v=v'+v_s\\v_s = v-v' = +8.0 - (-5.0) = +13 m/s`

So, the camera crew on the train observe Sydney moving at 13 m/s north