Question

A bullet of mass $ \, 20 \, g$ has an initial speed of $ \, 1 \, m \, s^{- 1}$ , just before it starts penetrating a mud wall of thickness $ \, 20 \, cm$ . If the wall offers a mean resistance of $ \, 2.5\times 10^{- 2} \, N,$ the speed of the bullet after emerging from the other side of the wall is close to:

• A. $0.7 \, m \, s^{- 1}$
• B. $0.3 \, m \, s^{- 1}$
• C. $0.1 \, m \, s^{- 1}$
• D. $0.4 \, m \, s^{- 1}$

Answer 1

Answer: (A)

$a=-\frac{2.5 \times 10^{- 2}}{20 \times 10^{- 3}}=-\frac{5}{4}ms^{- 2}$
From $v^{2}-u^{2}=2as$
$v^{2}=u^{2}+2as$
$v=\sqrt{1^{2} - 2 \times \frac{5}{4} \times 20 \times 10^{- 2}}$
$=\sqrt{0.5}$
$=0.7ms^{- 1}$