Question

A machine gun is mounted on a $2000\text{kg}$ car on a horizontal frictionless surface. At some instant the gun fires bullets of mass $10\text{gm}$ with a velocity of $500\text{m/sec}$ with respect to the car. The number of bullets fired per second is ten. The average thrust on the system is

• A. $550\text{N}$
• B. $50\text{N}$
• C. $250\text{N}$
• D. $250\text{Dyne}$

Answer 1

The correct option is B $50\text{N}$

$u=$ Velocity of bullet
$\frac{dm}{dt}=$ Mass thrown per second by the machine gun
= Mass of bullet $\times$ Number of bullet fired per second
$=10\text{g}\times 10\text{bullet/sec}=100\text{g/sec}=0.1\text{kg/sec}$
$\therefore$ Thrust $=u\frac{dm}{dt}=500\times 0.1=50\text{N}$