# A rotational problem

1. Dec 8, 2008

### iitjee10

1. The problem statement, all variables and given/known data
A stick of length L and mass M lies on a frictionless horizontal surface on which it is free to move in anyway.
A ball of mass m moving with speed v collides elastically with the stick at a distance d below its centre.
(a) Which quantities are conserved in this collision?
(b) What must be the mass of the ball so that it remains at rest immediately after collision?

2. Relevant equations

3. The attempt at a solution
Here if we conserve linear momentum,
we get mv=Mv1 (As the ball remains at rest.)
But I don't think this is right because if we conserve angular momentum, then we get something else, and if we conserve kinetic energy, then we get something else.

2. Dec 9, 2008

### tiny-tim

Hi iitjee10!

i] in any collision (with no external forces), both momentum and angular momentum are always conserved

ii] what does "elastically" mean?

3. Dec 9, 2008

### fluidistic

It means they collide with no loss of kinetic energy.

4. Dec 10, 2008

### iitjee10

elastically means coefficient of restitution is 1