Finding the Speed of a System of Three Bodies Before Collision

[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.

 

[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.

 

[orlan2r]

Its not easy. Please try it to solve

 

[sophiecentaur]

Its not easy. Please try it to solve

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

 

[orlan2r]

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

NO
more equation is needed

 

[Omega0]

NO
more equation is needed

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

 

[orlan2r]

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

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

 

[sophiecentaur]

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

Yep. Fair enough. Another equation is needed too.

 

[orlan2r]

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

Can you help me sophiecentaur?

 

[orlan2r]

Someone who can help me in this challenge problem?

 

[sophiecentaur]

Can you help me 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 realized how hard the problem appears to be. Is it a a level that's appropriate to the level of the course you're following?

 

[orlan2r]

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

 

[sophiecentaur]

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

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.
PF has had a number of threads about blocks on inclined planes (fixed and sliding), to give you a start with finding the sort of approach needed.

 

[orlan2r]

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.
PF has had a number of threads about blocks on inclined planes (fixed and sliding), to give you a start with finding the sort of approach needed.

AlreadyI did it. Only I wish to know the opinion of a specialist.
Could you propose this problem on other forum please. I can`t believe that nobody can propuse a solution.
Thanks