Energy/rotational mechanics question

[nehcrow]

Homework Statement

Check attached image.

Homework Equations

The rotational motion formulas
Ug = mgh

The Attempt at a Solution

Have no idea unfortunately :(

 

[gneill]

List the types of energy that will be involved and their basic formulas.
Are there any relationships between these energies? (hint: consider that the sphere is rolling without slipping).

 

[nehcrow]

OK, so kinetic energy and gravitational potential energy.
I got the first part correct, Ug = Mg(y - a)
but the 2nd part... not so much :\

 

[gneill]

You've missed out an important form of energy. Why do you suppose the problem gives you the expression for the moment of inertia of a solid sphere?

 

[nehcrow]

Rotational kinetic energy?
Sorry, I'm really lost when it comes to rotational mechanics, I need people to spell it out for me :(