A 3.8-kg sphere is suspended by a cord that passes over a 1.3-kg pulley of radius 3.5 cm. The cord is attached to a spring whose force constant is k = 86 N/m as in the figure below. Assume the pulley is a solid disk. (a) If the sphere is released from rest with the spring unstretched, what distance does the sphere fall through before stopping? The answer to this is .866 m. Not sure how to get it though. (b) Find the speed of the sphere after it has fallen 25 cm. Answer to this is 1.73 m/s. Not sure how to get this either. I'm not quite sure how to start this. I guess I'd use... 1/2kx2 for the spring, mgh since the sphere has PE before falling, 1/2mv2 for final KE of the falling sphere. And I'd have to do something about the pulley. I guess KE=Iω2 since its rotating? Not sure about that. And its a sphere that is falling and the I for a sphere is I=2/5mr2. Dont know if thats needed for this problem. Any help would be great. Thanks.