# Homework Help: Two spheres of are dropped to ground while in contact.

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1. Dec 22, 2017

### SiddhantRai

• Member advised to fill out the template, especially the attempt at solution, for all homework help requests.
Two spheres of different masses are dropped to ground.They are in contact as one above the other and are of masses, let’s say m and 2m.They are dropped with velocity v

- My question is if we can conserve momentum and if we can why?And how to find the final velocity of upper ball after collision with ground.

- (I have worked on the question because many of the regulators have said that I don’t show effort.)

- I’ve been thinking to use Impuse to calculate the velocity by calculating net Impulse on lower block. I’m stuck as I have three unknowns and only two eqations.

2. Dec 22, 2017

### phinds

and you have shown zero work here. When the moderators say you have not shown any effort, they mean exactly that. SAYING that you have made an effort is NOT showing the effort.

Last edited: Dec 22, 2017
3. Dec 22, 2017

### SiddhantRai

So please tell me what extra info you need. If you need some of my rough work I will post that. I just didn’t because I’m having trouble with the concept and don’t think it would matter.

4. Dec 22, 2017

### phinds

You have implied that you did some math. Show the math (and be sure to be clear about what it represents).

5. Dec 22, 2017

### haruspex

What are the conditions for the linear momentum of a system to be conserved?
What other physical laws might be useful?
What two equations?

Last edited: Dec 23, 2017
6. Dec 23, 2017

### haruspex

I am suspicious of these "two stacked balls" problems. The solution always seems to depend on treating the process as two separate collisions, the lower ball with the ground, then that bounced ball with the upper ball. How that is justified I am not sure.