# Homework Help: Simple Harmonic Motion

1. Jan 21, 2007

### suspenc3

1. The problem statement, all variables and given/known data

http://www.physics.umd.edu/courses/Phys122/Noyes/HW/hw1.pdf (pg 3)

2. Relevant equations

Im guessing that E = K + U has something to do with it

3. The attempt at a solution

Not really sure where to start..I tried a few approaches but none of them got me anywheres E = 1/2mv^2 + 1/2 kx^2..but im missing too many things..

Any help?

2. Jan 21, 2007

### Ja4Coltrane

when the bullet colides, it sticks. This means that energy is not conserved but something else is.

3. Jan 21, 2007

### Ja4Coltrane

by the way, the fact that the clay sticks and that the collision is therefore perfectly inelastic is one of those "assumptions"

Last edited: Jan 21, 2007
4. Jan 22, 2007

### suspenc3

conservation of linear momentum?

5. Jan 22, 2007

### Ja4Coltrane

yes. now you can use that in combination with energy.

6. Jan 22, 2007

### suspenc3

so I have $$\frac{mv +Mv_2}{m+M} = v_f$$ where $$Mv_2$$ is going to be 0 since it is at rest?

and $$E=1/2mv^2 + 1/2kx^2$$

Do i let m = m+M? and will 1/2kx^2 be 0 since the block can be considered to be at point x=0?...set it to zero and solve for v?

7. Jan 22, 2007

### Ja4Coltrane

you actually dont need to use energy untill you are ready to find the amplitude. You already have enough information to find the velocity.

8. Jan 22, 2007

### suspenc3

So imediately after the collision, the spring has no effect on the velocity?

9. Jan 22, 2007

### Ja4Coltrane

that's correct. two ways to understand that
1) imediately after colision, spring is not compressed and therefore applies no force.

2) even if it were compressed, a force causes an acceleration which only changes velocity of some period of time.

10. Jan 22, 2007

### suspenc3

Solved it..Thanks for the help

11. Jan 22, 2007

good job, np