# Homework Help: Relative motion of a dropping object on a moving train

1. Sep 5, 2009

### MechaMZ

1. The problem statement, all variables and given/known data
A bolt drops from the ceiling of a train car that is accelerating northward at a rate of 3.50 m/s2.
(a) What is the acceleration of the bolt relative to the train car?
(b) What is the acceleration of the bolt relative to the Earth?

3. The attempt at a solution
(a)10.4 m/s2 at 19.7° to the south from the vertical
(b)9.8 m/s2 vertically downward

I don't understand why the acceleration in (a) is not vertically downward since it is relative to the train. As we could assume the train is not moving, then the motion should be vertically downward isn't?

2. Sep 6, 2009

### Jebus_Chris

The train is accelerating. So the instant the bolt starts to drop you would see it going vertically downward if you were on the train. Now since the train is accelerating the bolt appears to be moving backwards since the train is speeding up but the bolt is not.