Homework Help: Finding the KE of a flywheel

1. Mar 2, 2012

clairecho22

1. The problem statement, all variables and given/known data
Q: A flywheel of moment of inertia 0.32kg/m^2 is rotated steadily at 120rad/s by a 50W electric motor. Find the kinetic energy of the flywheel.

2. Relevant equations
What is the best way to work this out? Am I using the right equations?
Can I simply substitute the angular rotation (120rad/s) instead of the velocity v in KE=(1/2)mv^2

3. The attempt at a solution
This is what I tried doing:
KE = (0.5).(m).(120)^2 but I still don't know the mass
Tried to use ω = v/r but I was not given the radius
To use power, I tried P = F.v -> P = m.a.v but I get stuck again because of mass and acceleration.

Where: ω = angular speed; v = linear velocity; m = mass; P = Power; F = force; KE = Kinetic Energy; a = acceleration

2. Mar 2, 2012

LawrenceC

The flywheel is only spinning, not translating. Use the appropriate formula.

3. Mar 2, 2012

xxChrisxx

You've been given some information that you've not used.
Why do you think you were given it?

You've got the linear formula, the principle is the same for rotation. You just need to use the rotational analogues.