In the arrangement shown a block of mass 2kg is pressed against a spring which is compressed by 10 cm and is applying a force of 80 N to the block. The spring is not attached to the block. The coefficient of friction is 0.5. When the block is released it moves up the plane by some distance and then comes back down. The kinetic energy of the block just before it starts compressing the spring again is

Question

G1 Physics · Accepted Answer

The spring constant is k=80/0.10=800 N/m, so initial spring energy is ½k(0.1)²=4 J. On the upward trip, (mg sin37°+µmg cos37°)s=4 gives s=0.2 m. On returning, K=(mg sin37°-µmg cos37°)s=(12-8)(0.2)=0.8 J. Hence C.