The potential energy of a spring when stretched through a distance x is 10 J. What is the amount of work done on the same spring to stretch it through an additional distance x?

Potential energy of the spring when stretched through a distance x,U' = 12kx2 = 10 JWhen x becomes 2x, the potential energy will beU' = 12k(2x)2 = 4×12kx2   = 4×10 = 40 JWork done = U' -U = 40 - 10 = 30 J