Q 11-05-181JEE MainJEE Main 2019 (10 Apr, Shift 2)Easy
A bullet of mass $20\ \text{g}$ has an initial speed of $1\ \text{m s}^{-1}$, just before it starts penetrating a mud wall of thickness $20\ \text{cm}$. If the wall offers a mean resistance of $2.5\times10^{-2}\ \text{N}$, the speed of the bullet after emerging from the other side of the wall is close to:
Answer: (A) $0.7\ \text{m s}^{-1}$
Work-energy theorem: $\tfrac12mv^2 = \tfrac12mu^2 - Fs$.
$$v^2 = 1 - \frac{2\times2.5\times10^{-2}\times0.2}{0.02} = 1 - 0.5 = 0.5 \;\Rightarrow\; v \approx 0.7\ \text{m s}^{-1}$$
Solution by Sreeraj P, M.Sc Physics