Question

A block A of mass m is attached by means of a spring to another block B of mass 4m and A is allowed to oscillate vertically on a pair of guide rails. If the upper block A is pressed down and released, then for what value of the compression would the lower block B just lose contact with the ground?

Answer 1

Suppose that the block of mass m is depressed by x1 and left so that the entire system just rebounds & loses contact with the ground.

Initially, there is a compression xo in the spring so that, kxo = mg

If the block B just loses contact, then the normal reaction becomes 0.