A relaxed spring with spring constant k = 60 N/m is stretched a distance di = 59 cm and held there. A block of mass M = 7 kg is attached to the spring. The spring is then released from rest and contracts, dragging the block across a rough horizontal floor until it stops without passing through the relaxed position, at which point the spring is stretched by an amount df = di/9. Ok, so there is three questions. a) In moving from the initial to the final position, by how much has the kinetic energy of the block changed? - I found out this is zero, since v = 0, for initial and final. (b) What is the work done by the spring? - This question is driving me insane. I know that potential energy equation for the spring is U = 1/2 k(Sf-Si)^2. So I tried with 1/2*60*(59)^2 - 1/2*60*(59-59/9)^2 = 103141 it was not the answer. also i tried with negative sign, I tried adding them, tried all kinds of possibilities, but all of them were not the answer. I think I should use different way to solve this problem. (c) What is the magnitude of the total work done by the frictional force? I guess I can figure this out once i know about the work done by the spring... (d) What is the magnitude of the frictional force on the block? This one could probably be solved once I know about c.. So my main question is how do I figure out the work done by the spring.