A relaxed spring with spring constant k = 70 N/m is stretched a distance di = 63 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/7.
W = F*d
KE = 1/2 k*x^2
KE = 1/2 m*v^2
The Attempt at a Solution
All I need is to find the change in kinetic energy, but i havent been able to get the right value yet.
I tried to find the change in kinetic energy by using 1/2kx^2, using .63 m as x, also trying 0.63 - 0.09 m as x, but i havent gotten the right value for change in KE.