What Happens to Two Blocks After an Elastic Collision on a Slope?

[DavidHarmon]

Homework Statement

A block of mass m = 2.80 kg slides down a 30.0° incline which is 3.60 m high. At the bottom, it strikes a block of mass M = 7.00 kg which is at rest on a horizontal surface, Fig. 7-41. (Assume a smooth transition at the bottom of the incline, an elastic collision, and ignore friction.)
http://img141.imageshack.us/img141/4472/741ue2.gif


(a) Determine the speeds of the two blocks after the collision.
Lighter Block:
Heavier Block:

(b) Determine how far back up the incline the smaller mass will go.

Homework Equations

v=final velocity
u= Initial velocity
a=acceleration
s= Displacement
v^2=u^2+2as

m1u1+m2u2=m1v1+m2v2

The Attempt at a Solution

I resolved to find acceleration perpendicular to the plain of motion and also the displacement, but as i was not given an initial velocity i cannot find out the final velocity of the small block as it hits the large block

Does anyone have any ideas as to how i would go about solving this question?

 

[DylanB]

i think you have to assume that the block starts at rest here.

to start, use energy conservation methods to find the velocity of the small block at the bottom of the incline.