A block of mass m is suspended from the ceiling of a stationary elevator through a spring of spring constant k.Suddenly the cable breaks and the elevator starts falling.Show that the block executes S.H.M of amplitude mg/k in the elevator. I solved the problem applying a pseudo force mg on the block in the opposite direction to that of the elevator. I would appreciate highly if someone can solve without applying pseudo forces. My solution:-As in the equilibrium position,the spring is stretched by mg/k,when we apply mg opposite to that of the weight,it instantly cancels the weight and only force left is kx and that makes it execute in S.H.M and mg/k is the extension when the block is at rest w.r.t. the elevator and so the amplitude.Please solve without pseudo force.Many thanks in advance.