Question

A bullet emerges from a barrel of length $1.2m$ with a speed of $640m{s}^{-1}$ . Assuming constant acceleration, the approximate time that is spent in the barrel after the gun is fired is

• A. $4ms$
• B. $40ms$
• C. $400\mu s$
• D. $1s$

Answer 1

Answer: (A)

Given, $s=1.2m,v=640m{s}^{-1},a=?,u=0;t=?$
We have the third equation of motion
$2as=v^2-u^2$
$2a\times 1.2=640\times 640$
Or $a=\frac{8\times 64\times 10^3}{3}$
And by first equation of motion
$v=u+at$
Or $t=\frac{v}{a}=\frac{15}{4}\times 10^{-3}$
$=3.75\times 10^{-3}s\approx 4ms$