# Homework Help: Forces in motion

1. Nov 20, 2004

### futb0l

Got this out of my book .. had no idea how to do it.
Here's the exact question...

An old light globe hangs by a wire from the
roof of a train. What angle does the globe
make with the vertical when the train is accelerating
at 1.5 m s−2?

Thanks guys.

2. Nov 20, 2004

### Galileo

When the train is accelerating with accelration a, it's no longer an inertial frame.
It looks like all objects in this frame are subjected to an apparent force F=-ma.

So just act like there's a horizontal force -ma acting on the globe.

3. Nov 20, 2004

### BobG

Simple trig. What's the force and direction of gravity? What's the force and direction of the train's acceleration? Apply the Pythagorean theorem to get the magnitude and look at your trig relationships (SOHCAHTOA).

4. Nov 20, 2004

### primarygun

I think the length of the rope is also a factor.

5. Nov 22, 2004

### futb0l

Thanks BobG!

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook