Preparing for Physics Final: Solving Homework Equations

[penguinnnnnx5]

Homework Statement

Currently studying for a physics final on Wednesday 12/12/12
The problem can be found here

Homework Equations

Not very sure.

v_fball=(v₀(m_ball-m_plank)+2m_plankv_0,plank)/(m_ball+m_plank)
m_ballv₀=(m_ball+m_plank)v_f

The Attempt at a Solution

I have no idea how to do a. I've tried
v_fball=(v₀(m_ball-m_plank)+2m_plankv_0,plank)/(m_ball+m_plank)
But it just comes to 0.

b.
I've thought about it and the only possible way to get the answer given that I can think of is this:
m_ballv₀=(m_ball+m_plank)v_f
mv₀=2mv_f
v_f=v₀/2

Does this involve angular momentum as well? Or inertia? Any help would be gratefully appreciated!

 

[gneill]

Yes, angular momentum is involved, as is rotational KE. So, start by writing all the conservation equations.