Q. A disc of mass 10 g is kept floating horizontally in air by firing bullets, each of mass 5g , with the same velocity at the same rate of 10 bullets per second. The bullets rebound with the same speed in positive direction. The velocity of each bullet at the time of impact is
A) $196\ cms^{- 1}$
B) 98 $cms^{- 1}$
C) 49 $cms^{- 1}$
D) 392 $cms^{- 1}$
Explanation
(b) $2mnv = Mg$
$v = \frac{Mg}{2mn}$
or $= \frac{10 \times 980}{2 \times 5 \times 10}cms^{- 1}$
$= \frac{9800}{100}cms^{- 1}$
$= 98\ cms^{- 1}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.