Conservation of Momentum Law- Recoil Velocity (Question)

[seeindubble12]

First time posting, I hope I do this correctly!

I am struggling to grasp this concept. This is my attempt at solving. If I am completely off base, will some explain to me again how it works. Our instructor explained it to us with a very detailed formula which, I must confess, has caused me more than a little anxiety because I am not following! Thanks for the help!

1. Rifle (suspended by strings) - 2kg; fires bullet of 0.01 kg at speed of 200 m/s. What is the recoil velocity of the rifle?



2. (mv) + (mv) = (M + m)(v)



3. (0.01)(200) + 0 = (0.01 +2)(v)
2=2.01(v)
divide both sides by 2.01, and the answer is v= .99

 

[Doc Al]

This isn't quite right.

Momentum is conserved. What's the total momentum of the system (rifle + bullet) initially? What's the total momentum of the system after the bullet is fired?

Set that total momentum equal to m1v1 + m2v2.