Question

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

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

Answer 1

Answer: (B)

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