# Rifle Momentum problem

1. Oct 9, 2007

### Zerobu

1. The problem statement, all variables and given/known data
A rifle with a weight of 30N fires a 5.0g bullet with a speed of 300 m/s

(a) Find the recoil speed of the rifle

(b) If a 700 N man holds the rifle firmly against his shoulder, find the recoil speed of the man and the rifle

2. Relevant equations
i think this problem has something to do with the conservation of momentum equation but i am not sure

3. The attempt at a solution
I have no idea how to even begin this problem

2. Oct 9, 2007

### Count Iblis

Momentum of the bullet is 5.0g times 300 m/s, right? So the momentum of the riffle is the same but in the opposite direction. What is the mass of the rifle given that the weight of the rifle is 30 N? Momentum of the rifle is the mass of the rifle times its velocity...

3. Oct 17, 2007

### tru_royalty

Total velocity before firing = 0...Momentum of the rifle must be equal but opposite to that of the bullet, ie. (0.005kg*300m/s)+(3kg*v)=0, and v= -0.5m/s... I ain so sure bout tha second part, but I think you'll just combine the masses of the rifle and the man (70kg), and find the v in the same way...can anyone correct me if I'm wrong? We're just starting this topic...