Question

A bullet is fired into a wooden block with a speed of 350 m/s and it emerged out in 0.1 secs after entering the block with a velocity of 50 m/s. what is the thickness of the block?
(Assume that the wooden block offers a constant resistance to the bullet.)

URGENT!

Answer 1

Initial speed of the bullet $\sf{=350\ m\,s^{-1}.}$

Time taken for coming out of the block $\sf{=0.1\ s.}$

Speed of bullet when it comes out of block $\sf{=50\ m\,s^{-1}.}$

By first equation of motion, the retardation offered to the bullet by the block is,

$\longrightarrow\sf{a=\dfrac{v-u}{t}}$

$\longrightarrow\sf{a=\dfrac{50-350}{0.1}}$

$\longrightarrow\sf{a=-3000\ m\,s^{-2}}$

The thickness of the block is the same as the displacement travelled by the bullet during this time.

Hence by third equation of motion, the thickness of the block is,

$\longrightarrow\sf{s=\dfrac{v^2-u^2}{2a}}$

$\longrightarrow\sf{s=\dfrac{50^2-350^2}{2\times-3000}}$

$\longrightarrow\sf{s=\dfrac{2500-122500}{2\times-3000}}$

$\longrightarrow\sf{s=\dfrac{-120000}{-6000}}$

$\longrightarrow\sf{\underline{\underline{s=20\ m}}}$

Hence 20 m is the answer.