posted by Abbey .
A bullet with mass 0.40 kg is fired with an initial velocity of 400 m/s from a gun with mass 5.0 kg. The speed of the reoil of the gun is?
Do I have to 0.40 and 5.0 an then divide that by 400?
No. The bullet's momentum (0.40)x400 equals the recoiling gun's momentum (in the opposite direction.
That makes the recoil velocity 0.40*400/5.0