Question

a rifle with a weight of 30 N fires a 5.0-g 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 hisshoulder, find the recoil speed of the man and rifle.

Answer 1

Mr*Vr= Mb*Vb

Vr= Mb*Vb/Mr = .005*300/3.068 = .489m/s

so... you are correct, and the sign is negative as you said.

For b), it looks like the mass is just substantially greater, since the man and the rifle are in contact and presumably move together.

V = Mb*Vb/(Mr+Mm) = .005*300/(3.068+71.59) = -.02m/s