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 it spends in the barrel after the bullet fired is:

• A. $40ms$
• B. $4ms$
• C. $4second$
• D. $0.4second$

Answer 1

Answer: (B)

Length of the barrel $=1.2m$
Speed of the bullet $=640m{s}^{-1}$
According to the third equation of motion
$V^2=u^2+2as$
$V^2=0+2as$
$640\times 640=2\times a\times 1.2$
$\frac{320\times 640}{1.2}=a$
$640=0+\frac{640\times 320}{1.2}\times t$
$t=\frac{1.2\times 640}{640\times 320}t=0.0037=t$
$=3.7\times 10^{-3}t\approx 4ms$