# I How would you include gravity in a momentum problem?

1. Sep 25, 2016

### Rnotaria

Say you have a big ball of mass m1 and a little ball on top of that of mass m2 (assume they are a small distance apart, like 1mm). Now lets drop these from a height of h so that the big ball will bounce off the ground and collide into the little ball in an elastic collision.

Now I know gravity would play a key role in this example but how would you perform calculations with it? I know F=p/t and momentum will not be conserved since there is an external force (gravity) so knowing this, how can you determine how high each ball will rise after the collision?

2. Sep 25, 2016

### phinds

How would you start on this problem? And by the way, in reality, "bouncing off the ground" is hardly an elastic collision.

Is this a homework problem? If so, you need to put it in the homework section and use the template.

3. Sep 25, 2016

### Rnotaria

This was just an example I thought of because all the problems I've done so far have pretty much been absent of external forces (such as a car collision).

4. Sep 25, 2016

### phinds

OK, then I ask again. How would you start on this problem?

5. Sep 25, 2016

### Staff: Mentor

It's still a homework problem - the Homework Forums are for all such problems, whether they came to you as part of formal classwork or as self-study.

I am closing this thread, but I encourage you to start a new thread in the "Introductory Physics Homework" forum and use the template. The process there is designed for this sort of problem.