physics
posted by Lynn .
A 2.8kg block is hanging stationary from the end of a vertical spring that is attached to the ceiling. The elastic potential energy of the spring/mass system is 1.2 J. What is the elastic potential energy of the system when the 2.8kg block is replaced by a 5.4kg block?

The elastic spring energy is related to distance stretched squared. But distance stretched is proportional to force.
Here force doubles, so distance stretched doubles, so PE in the spring doubles squared.