# Homework Help: Spring Problem (Urgent)

1. Oct 6, 2008

### dsptl

Last edited by a moderator: May 3, 2017
2. Oct 6, 2008

### Hootenanny

Staff Emeritus
Saying that you have no idea doesn't count as an attempted solution. Have you read your class notes and/or text?

3. Oct 6, 2008

### dsptl

my professor doesn't go in details and book is to consusing but still I will give a try:

attempt: First I thought to use

W = delta KE + delta PE

but I was confused b/c i did not see a way to put those spring forces in there

so i was kindly asking for a help

4. Oct 6, 2008

### Hootenanny

Staff Emeritus
Thank you for trying, your threads will generally get answered a lot quick if you show an attempted solution.

You're right to approach the problem using conservation of energy. You know that the work done by friction and the 400 N/m spring must be equal to the energy stored in the N/m spring.

Can you go from here?

5. Oct 6, 2008

### dsptl

is it like this:

F x S = Ef - Ei

6. Oct 6, 2008

### Hootenanny

Staff Emeritus
We'll take it a step at a time. What is the energy stored in the 200N/m spring before the block is released?

7. Oct 6, 2008

### dsptl

= .5k(x.x) + .5mv.v + mgh

8. Oct 6, 2008

### Hootenanny

Staff Emeritus
Could you explain how each of the terms arise, what does each term represent?

9. Oct 6, 2008

### dsptl

1st is spring force , 2nd is kinetic energy and 3rd is potential enery, which is 0.

10. Oct 6, 2008

### Hootenanny

Staff Emeritus
Good. What about the kinetic energy, is that non-zero before the block is released?

11. Oct 6, 2008

### dsptl

i think it is zero since Vi is 0

12. Oct 6, 2008

### Hootenanny

Staff Emeritus
Correct. So, the total energy of the system is simply the energy stored by the spring, can you calculate it?

Now, when the block reaches the 400N/m spring is compresses it. So how much energy is stored in this spring? Can you also calculate this value?

13. Oct 6, 2008

### dsptl

at intial = .5(200N/m)(.1 x .1) = 1N

at Final = .5(4000N/m)(.05 x .05) = .5 N

14. Oct 6, 2008

### dsptl

do i just add them together?

15. Oct 6, 2008

### Hootenanny

Staff Emeritus
No.

You started off with this much energy:
And ended up with this much energy:
Where did the rest of the energy go?

You also need to be careful with your units, the Newton is not a measure of energy.