Question

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

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

Answer 1

Answer: (A)

Given, $s=1.2 \, m, \, v=640 \, m s^{- 1}, \, \, a=?, \, \, u=0;t=?$
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 4 \, ms$