Energy and Simple Harmonic Motion

[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
Help me please!

[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?

[Pius]

it is not moving, x=0?

[Pius]

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

[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?

[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....