# System from three bodies

1. Jul 5, 2015

### orlan2r

The figure shows a system consisting of two identical spheres of mass m and a mobile platform mass M. If the system starts from rest in the position shown in the figure, what is the speed from each sphere in the moment when both move horizontally, before the crash occurs. Neglect all friction.

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2. Jul 5, 2015

### sophiecentaur

This looks lie a homework type question. Easy(ish) to solve if you remember that the PE at the start becomes KE at the end.

3. Jul 5, 2015

### orlan2r

Its not easy. Please try it to solve

4. Jul 5, 2015

### sophiecentaur

I will have a go this evening if time permits. Is it really not just the conservation laws that solve it? (Momentum too)

5. Jul 5, 2015

### orlan2r

NO
more equation is needed

6. Jul 5, 2015

### Omega0

What else equations? It is obvious that Newtonion physics is sufficient... you have not even friction!

7. Jul 5, 2015

### orlan2r

Conservation of momentum on the x axis and conservation of energy (2 equations but three unknown speeds)

8. Jul 5, 2015

### sophiecentaur

Yep. Fair enough. Another equation is needed too.

9. Jul 8, 2015

### orlan2r

Can you help me sophiecentaur?

10. Jul 8, 2015

### orlan2r

Someone who can help me in this challenge problem?

11. Jul 9, 2015

### sophiecentaur

Sorry about this but it requires a lot of time, I think. Afaics, you would need to write out the equation of motion, from t = 0, for all three bodies and arrive at an integral which has to be solved. To make it harder, the limits for the short fall will be different from the long fall.
BTW, who has set you this beastly problem? Perhaps you could go back and ask for guidance??? After all, they really should be able to help - if they have actually realised how hard the problem appears to be. Is it a a level that's appropriate to the level of the course you're following?

12. Jul 11, 2015

### orlan2r

This problem I have created myself. Who do you think could help me?

13. Jul 12, 2015

### sophiecentaur

If it your own problem then perhaps you should start from the beginning, with a simpler situation and work up to your OP.
Start with a single ball on a linear slope, then a single ball on a circular slope.