# Energy and Simple Harmonic Motion

1. Feb 19, 2009

### Pius

1. The problem statement, all variables and given/known data

A 3.2-kg block is hanging stationary from the end of a vertical spring that is attached to the ceiling. The elastic potential energy of this spring/mass system is 1.8J. What is the elastic potential energy of the system when the 3.2-kg block is replaced by a 5.0-kg block?

2. Relevant equations

Elastic potential energy=1/2kx^2
Gravitational potential energy=mgh

3. The attempt at a solution

2. Feb 19, 2009

### CompuChip

The problem is that you have the extension x of the spring in your formula, which you do not know. However, there is an extra clue in the word "stationary". What does that mean?

3. Feb 19, 2009

### Pius

it is not moving, x=0?

4. Feb 19, 2009

### Pius

What should I put in for h and k? Thank you, CompuChip!

5. Feb 19, 2009

### CompuChip

Exactly, it is not moving. But that does not mean that x = 0 (then the spring would be in its equilibrium position... but it is stretched by the mass that's hanging on it)... it merely says that x is a constant. But what can you say about the net force acting on the block. Which forces are there?

6. Feb 24, 2009

### skiing4free

'x' is the extension from the equilibrium point in the spring when the 3.2kg mass is changed to 5kg. Because 'g' and 'k' stay constant it is just simple ratios....