# Homework Help: Kinetic energy of massless spring

1. Nov 26, 2004

### Flinthill84

Alright I'm having a little trouble on this one...

One end of a massless spring is welded to a flat surface; the other end points upward. A mass of 2.0kg is set on top of the spring. The spring is then compressed by hand so that the end of the spring is 42cm lower than the position of the spring with no mass on top. The spring is then seddenly released. What is the maximum kinetic energy of the 2.0kg mass??

I think i use the formula KE=1/2mv^2, if that is true could anyone give me a hint on how to find the velocity please? Thankyou!

2. Nov 26, 2004

### Parth Dave

The spring will have some potential energy. This potential energy will all be converted into kinetic energy for the block. You need to find out how much potential the spring has.

3. Nov 26, 2004

### Flinthill84

ok so the potential energy would be U=mgh which would be (2.0kg)(9.8m/s^2)(-0.42m)...but I guess I still don't understand how this plays into the kinetic energy?

Last edited: Nov 26, 2004
4. Nov 26, 2004

### misogynisticfeminist

^ conservation of energy? every joule of potential energy being converted into kinetic energy.

just equate $$E_k = E_p$$

5. Nov 26, 2004

### Flinthill84

so mgh=1/2mv62 and then I could solve for v and finally solve for kinetic energy?? Or are you saying that the amount of potential energy that I found is the amount of kinetic energy?

Last edited: Nov 26, 2004