Question

In a fight, a man fires 50g bullets from a machine gun, each at a speed of 1.0 km/s. If he fires 20 bullets in 4 seconds, what average force does he exert against the machine gun during this period?

• A. 250 N
• B. 327 N
• C. 292 N
• D. 178 N

Answer 1

The correct option is B

327 N

The momentum of each bullet = $0.050kg\times 1000m/s=50kgm/s$
The gun is imparted this much of momentum by each bullet fired. Thus, the rate of change of momentum of the gun =$\frac{50kgm/s\times 20}{4s}=250N$
To hold the gun a man must exert a force of 250 N against the gun.