# Homework Help: Blocks on Spring without Friction

1. Jun 15, 2011

### wolves5

A spring is stretched a distance of Dx = 40 cm beyond its relaxed length of xo by a force, F = 20 N. Attached to the end of the spring is an block of mass m = 12 kg, which rests on a horizontal frictionless surface.
After a moment, the force is removed.

a) What is the potential energy of the block due to the spring when it is held in the stretched position?

For this question, I did PE=(mgh). So, PE= (12)(9.8)(0.4m) and got 47.04 J, but thats not the right answer.

b) What is the total mechanical energy of the block when it is held in the stretched position?

c) What is the total mechanical energy of the block when it returns to its unstretched position?

d) When the spring again returns to its unstretched length, what is the speed of the block?

e) What is the total mechanical energy of the block when it has returned only halfway (20 cm) to its unstretched position?

f) When the spring has returned only halfway (20 cm), what is the speed of the block?

2. Jun 16, 2011