# Homework Help: Work with spring force

1. Oct 20, 2008

### blayman5

1. The problem statement, all variables and given/known data
A spring with spring constant of 29 N/m is
stretched 0.21mfromits equilibrium position.
How much work must be done to stretch it

2. Relevant equations
W=-kx(x)/2

3. The attempt at a solution
I solved it and got 0.4263 and it was wrong. does it need to be negative?

2. Oct 20, 2008

### LowlyPion

How did you arrive at that number?

3. Oct 20, 2008

### blayman5

i did ((29)(0.21)(0.14))/2 =0.4263. does it need to be negative?

4. Oct 20, 2008

### LowlyPion

That's not quite right.

Additional work = Difference in work = 29*(.21+14)2/2 - 29*(.21)2/2

5. Oct 20, 2008

### blayman5

Ok so that means it would equal
29*(.21+14)2/2 - 29*(.21)2/2 =1.1368

Thanks

6. Oct 20, 2008

### LowlyPion

That's what I got anyway. What you need to remember is that work is the area under the force and distance curve over the range of the curve.

Cheers

7. Oct 20, 2008

### blayman5

i will remember thanks

8. Oct 21, 2008

### dleccord

wait...

wait wait... why is it 14 instead of .14?

9. Oct 21, 2008

### LowlyPion

He got the right answer and the 14 was apparently a typo. Calculate it out and you will see the inner sum needs to sum to .35.