# Homework Help: Ball moving up a wedge

1. Aug 22, 2007

### raffish

1. The problem statement, all variables and given/known data
a ball with mass m and velocity v is moving up a wedge of mass M. What height does the ball reach if:
a) the ramp is fixed on the table
b) the ramp is able to move on a frictionless surface

2. Relevant equations
mgh
(1/2)mv(squared)

3. The attempt at a solution
for a) i just solved for h using both equations given above, since there is a loss in kinetic energy which is converted to a gain in gravitational potential energy as the ball moves up the wedge. so this gives me that the h = v(squared)/2g.
im stuck on b) however.

2. Aug 22, 2007

### Astronuc

Staff Emeritus
If the ramp is supported by a 'frictionless' surface, then as the ball of mass m goes up the ramp, it imparts a force on the ramp, and that force is related the weight.

So now the ball of mass m is doing work on the ramp of mass M, and both accelerate.

Think about using conservation of momentum in addition to conservation of energy.

3. Aug 22, 2007

### raffish

well that was sort of my train of thought as well. the ball will exert a force onto the wedge thus making both move.
we know that v'2 (that is the new velocity of the wedge with mass M) = (2M/m+M) * v1 (that is the original velocity of the ball)

but im confused because isnt the angle a factor aswell, i mean the force exerted on the wedge by the ball is different depending on how steap it is.
i mean taken the extreme case we could say the wedge is in fact block, in that case i can see the conservation of momentum as given above applying to this situation, but in a case where the angle is flat the force exterted on the wedge would be less, or at least thats what im thinking.