# Homework Help: Question about a spring

1. Jul 20, 2012

### cragar

1. The problem statement, all variables and given/known data
The left end of a spring is attached to a wall. When bob pulls on the right end with 200N force,
he stretches the spring by 20cm. The same spring is then used for tug of war between bob and Carlos. Each pulls on the spring with a 200N force. How far does Carlos's end of the spring move? explain
3. The attempt at a solution
If I think of this as the spring hanging in a gravitational field. I put a weight on it that was 200 N it will pull it down 20cm. but if my spring is hanging on a nail, that is also providing a force of 200N in the opposite direction. So i think that the spring will be stretched still by 20cm. Although I am not sure if it will be stretched by 10cm at Carloss's end or zero.

2. Jul 20, 2012

### TSny

Yes, the spring will still stretch a total of 20 cm. I think the two guys are assumed to move equal distances.

3. Jul 20, 2012

### pgardn

Maybe you want to do this in the horizontal to make it easier. (No gravity)

Also you might want to ask yourself how hard the wall pulls on the spring before Carlos comes into play.

Oops I see someone has already posted. I will now kindly drop out.

4. Jul 20, 2012

### TSny

Hi, pgardn. Don't drop out. The more the merrier!

5. Jul 20, 2012

### cragar

so then each person will move 10cm

6. Jul 20, 2012

### PeterO

Probably - but you can certainly be sure the ends of the spring will be 20cm further apart.

The common, incorrect response to this question is that each move 20cm - as I said, and you seem to realise, that answer is incorrect.

7. Jul 20, 2012

### TSny

I second that.

8. Jul 20, 2012

### pgardn

I was just going to replace the wall with Carlos. And there you have it.

All is in order.

9. Jul 20, 2012

### azizlwl

Using work-energy analysis could also be used.