Question

A bullet emerges from a gun barrel of length $1.2m$ with a speed of $640m/s$. Assuming constant acceleration, the approximate time that it spends in the barrel after the gun is fired is

• A. $3.75\times {10}^{-3}s$
• B. $4.5\times {10}^{-3}s$
• C. $5\times {10}^{-3}s$
• D. $1.75\times {10}^{-3}s$

Answer 1

The correct option is A $3.75\times {10}^{-3}s$

$s=1.2\text{m},v=640\text{m/s},a=?;u=0;t=?$
Using $2as=v^2-u^2$, we get
$\Rightarrow 2a\times 1\cdot 2=640\times 640\Rightarrow a=\frac{8\times 64\times {10}^3}{3}$

Using $v=u+at,$ we get:
$t=\frac{v}{a}=\frac{15}{4}\times {10}^{-3}=3.75\times {10}^{-3}$
$=3.75\times {10}^{-3}s$

Hence, the correct answer is option (a).