# I Work Problem

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1. Jan 28, 2017

### iPhotonHQ

"It takes 100J of work to stretch a spring 0.5m from its equilibrium position. How much work is needed to stretch it an additional 0.75m."
Attempt: w = ⌠abF(x)dx
work = F x D
100J = F x 0.5m
F = 200J

0.75 + 0.5 = 1.25
w = ⌠0.51.25 200dx
w = 150 J

The correct answer: w = 525 J

what did I do wrong? Thanks!

Nevermind, I found the exact problem online, so sorry!

2. Jan 28, 2017

### Arman777

Work is not constant in spring.You cant use W=Fd.You should take an integral
(Carefull for the signs when you take an integral).
Another thing that Questions ask "The work done by our force".

3. Jan 28, 2017

### iPhotonHQ

My problem was that I forgot hooke's law.
F = kx
I can apply it to the given information to find the target solution.

4. Jan 28, 2017

### Arman777

Any ideas How ?

5. Jan 28, 2017

### iPhotonHQ

w = ⌠.51.25 kx dx
you can solve for k by plugging in known integral...
100 = ⌠0.5kxdx

you should get k = 800

6. Jan 28, 2017

great