The spring shown in figure (12-E5) is upstretched when a man starts pulling on the cord. The mass of the block is M. If the man exerts a constant force F, find (a) the amplitude and the time period of the motion of the block, (b) the energy stored in the spring when the block passes through the equilibrium position and (c) the kinetic energy of the block at this position.
a) we know
b) The energy stored in the spring when the block passes through the equilibrium position
c) At the mean position, potential energy is zero, so