physics

A mass of 1.00kg is dropped from a height of 80cm onto a spring, of unstretched length of 20.0cm, which is resting on the floor. It comes to rest, momentarily, at a height of 10.0cm from the floor. If we can ignore friction, find the spring constant of the spring. I feel like spring questions are so confusing. I'm not even sure what to do. I calculated -Wgravity=mgDELTAy= 7.84J Now, can I equate -Wgravity=Uelastic=1/2kx^2? I'm so confused.