Question

A person holding a rifle stands on a smooth surface and fires 10 shota horizontally in 5 secs . Each bullet has a mass of 10 gm with a muzzle velocity of 800 metre per sec . Final velocity and force are?

Answer 1

We have to use the Law of momentum conservation:

P ( initial ) = P ( final )

0 = n · m · u + ( M - n · m ) · v

where: n = 10, m = 10 g = 0.01 kg, u = 800 m/s, M = 100 kg.

0 = 10 · 0.01 kg · 800 m/s + ( 100 kg - 10 · 0.01 kg ) · v

v = - 80 kgm/s / 99.9 kgm/s

v = 0.8 m/s

Then : F = Δ P / Δ t = ( 10 · 0.01 kg · 800 m/s ) : 5 s = 16 N

Answer: The average force exerted on the person is 16 N.