Question

A machine gun is mounted on a 2000 kg car on a horizontal frictionless surface. At some instant, the gun fires 10 bullets/second, each of mass 10 g with a velocity of 500 m s${}^{-1}$. The acceleration of the car is

• A. 0.025 ms${}^{-2}$
• B. 0.25 ms${}^{-2}$
• C. 0.5 ms${}^{-2}$
• D. 500 ms${}^{-2}$

Answer 1

The correct option is A 0.025 ms${}^{-2}$

$M_{car}=2000kg$

$n=10bullets/s$

$M_b=10g=0.01kg$

$V_b=500m/s$

Momentum of each bullet $=0.01\times 500$

$\left(M_b{V}_b\right)P_b=5kgm/s$

Force on car $=n{P}_b$

$50kgm/s^2$

$F_{car}=50N$

$a_{car}=\frac{50}{2000}=\frac{1}{40}$

$a_{car}=0.025m/s^2$