question_answer

A dish of mass 10 gm is kept horizontally in air by firing bullets of mass 5 g each at the rate of 10 per sec. If the bullets rebound with the same speed, what is the velocity with which the bullets are fired?

A)  49 cm/sec

B)  147 cm/sec

C)  98 cm/sec  

D)  196 cm/sec

Correct Answer: C

Solution :

 Weight of the dish\[=\frac{10}{1000}\times g\] Speed of the bullet \[=v\] Rate of change of momentum of bullets             \[=\frac{2\times 10\times 5}{1000}v\]\[=\]applied force on the dish Now,\[\frac{2\times 10\times 5}{1000}v=\frac{10\times g}{1000}\] \[\therefore \]      \[v=0.98\,\,m/s=98\,\,cm/s\]