Q 11-04-045NEETJEE MainMedium
A horizontal jet of water with cross-sectional area $2\ \text{cm}^2$ and speed $20$ m/s strikes a vertical wall and falls dead (does not rebound). The force on the wall is (density of water $= 1000\ \text{kg/m}^3$)
Answer: (B) $80$ N
Concept. Water hitting per second $\rho Av$, each losing momentum $v$: $F = \rho Av^2$.
Step 1. Substitute. $1000 \times 2 \times 10^{-4} \times 400 = 80$ N.
Answer. $80$ N (Option B).
Solution by Sreeraj P, M.Sc Physics