in elevator before cable break mg=kx in frame of elevator after cable break F(gravity)+F(pseudo)+F(spring)=0 answering question is not tough but i am interested in other things that will happen with this system. Will the elevator move with a constant acceleration with respect to a person standing on the surface of earth.???? (If mass of block attached to spring and elevator are comparable.) I think elevator will not move with constant acceleration ; but the center of mass of spring mass plus elevator will move with constant acceleration. since acceleration of spring block is not g (acceleration due to gravity) so elevator will not move with constant acceleration... How will you define the motion of block after cable breaks (with respect the earth's frame)??? I can't do this.