Physics
posted by Sarah .
A potter’s wheel with rotational inertia of 45 kg m2, is spinning freely at 40 rpm. The potter drops a lump of clay onto the wheel where it sticks a distance 1.2 m from the rotational axis at the wheel’s center. If the subsequent angular speed of the wheel is 32 rpm, what is the clay’s mass? (Hint: treat the clay as a point object, so I=mr2)

Well, final angular momentum is equal to intial.
wf*If=wi*Ii
where If= Ii+ mr^2 so solve for m
change w to rad/sec 
conserve angular momentum
45 * 40 = (45 + m * 1.2^2) * 32
(no need here to convert rpm to radians per second)