# Homework Help: Spring pic included!

1. Dec 14, 2008

### hodgepodge

1. The problem statement, all variables and given/known data
A 20 gram bullet strikes a 15 kg mass attached to a spring. The mass slides and compresses the spring by 12 cm. Calculate the velocity of the bullet initially. (No Friction!)

k=200n/m

bullet mass spring
=D I---------I II
I ICCCCCCCCCII
____I________I__________II

sorry after i posted it i realized how messed up the pic was

Last edited: Dec 14, 2008
2. Dec 14, 2008

### Mthees08

Hint: Momentum is always conserved

secret hint: Energy is not conserved, until after the bullet is embedded in the block.

3. Dec 14, 2008

### hodgepodge

does my answer of 10.88995 m/s seem correct?

4. Dec 14, 2008

### Mthees08

Not what I got, and it isn't simply off by an order of 10^n it just seems wrong. Check your computations, make sure you used the correct formula for Ke of a spring. and one more hint, work the problem backwards. Find the Energy at the end and work back until the point of the initial block's velocity, and then yaddi yaddi yadda.

5. Dec 15, 2008

### Dell

does the bullet stay in the block?