Question

If the bullet penetrates the block to a depth of $3.0cm$, the approximate average force of resistance by the block of wood is :

• A. $8.2\times {10}^{4}N$
• B. $32.4\times {10}^{4}N$
• C. $64.8\times {10}^{4}N$
• D. $16.8\times {10}^{4}N$

Answer 1

The correct option is D $16.8\times {10}^{4}N$

$v^2-u^2=2as\Rightarrow 0-{502}^2=2\times a\times \frac{3}{100}$
$\Rightarrow a=-\frac{{502}^2\times 100}{2\times 3}\cong 4.2\times {10}^{8}m/s$
$\overrightarrow{F}=m\overrightarrow{a}=\frac{40}{1000}\times 4.2\times {10}^8=16.8\times {10}^{4}N$