# Basic Questions

1. Mar 17, 2009

### davidliebehar

Here is a very basic question that I need help with.

1. The problem statement, all variables and given/known data
A spring has a spring constant (k) of 82 N/m. How far must the spring be compressed to store 35J of potential energy?

2. Relevant equations
I think it is: E = 1/2 kx^2

3. The attempt at a solution

2. Mar 17, 2009

### LowlyPion

Welcome to PF.

Let's see. You have the equation. They tell you what E is. They tell you what k is ... so you're having trouble solving for x?

3. Mar 17, 2009

### davidliebehar

yes.
should the equation look like this?
35J = 1/2 (82 N/m) x^2

4. Mar 17, 2009

### LowlyPion

Just solve for X.

5. Mar 17, 2009

### davidliebehar

I don't know how to.
is 82 N/m the same as 82 J?

would I get

35J divided by 41 N/m = x^2? then x = square root of 35J divided by 41 N/m?

6. Mar 17, 2009

### LowlyPion

No N/m is a spring constant. It moves 1 meter for every 82 Newtons of force.

Joules are units of what? N-m? and you are dividing by N/m? that yields m2 and x2 is m2 ... so everything is right.

As to your calculation ... that's right.

7. Mar 17, 2009

### davidliebehar

i dont know whAt to do
plaese show me exactly how to solve this problem and all the steps i am so lost

8. Mar 17, 2009

### LowlyPion

Look. You've already solved it ... that is if you meant to divide 35 by 41 before you took the square root.

9. Mar 17, 2009

### davidliebehar

i just want an answer in meters.

10. Mar 17, 2009

### LowlyPion

That gives you an answer in meters.

11. Mar 17, 2009

### davidliebehar

(sqaure root of 35j divided by 41 N/m) meters?

12. Mar 17, 2009

### LowlyPion

sqaure root of (35j divided by 41 N/m) meters?

Yes. I already showed you that you get m2 before you take the square root.

13. Mar 17, 2009

### davidliebehar

thanks for your help, but i still cant understand this, i'll have to ask my instructor.