Q 11-04-018NEETJEE MainEAMCET 2007 (Engineering)Easy
A rifle of $20$ kg mass can fire $4$ bullets per second. The mass of each bullet is $35 \times 10^{-3}$ kg and its final velocity is $400\ \text{m s}^{-1}$. Then, what force must be applied on the rifle so that it does not move backwards while firing the bullets?
Answer: (D) $56$ N
Concept. Force $=$ rate of momentum given to the bullets: $F = nmv$.
Step 1. Substitute. $4 \times 0.035 \times 400 = 56$ N (rifle mass not needed).
Answer. $56$ N (Option D).
Solution by Sreeraj P, M.Sc Physics