Answer:
The speed is 13 m/s
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 [tex]v' = -5.0 m/s[/tex] 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
[tex]v = +8.0 m/s[/tex] (positive because it's moving north)
So, we can find Sydney's velocity with respect to the frame O' as follows
[tex]v=v'+v_s\\v_s = v-v' = +8.0 - (-5.0) = +13 m/s[/tex]
So, the camera crew on the train observe Sydney moving at 13 m/s north