Question

A bullet of mass $20g$ moving with a speed of $75m{s}^{-1}$ hits a fixed wooden plank and comes to rest after penetrating a distance of $5cm$. What is the average resistive force exerted by the wooden plank on the bullet?

Answer 1

mass, m = 20g (0.02kg)

initial velocity, u = 75m/s

final velocity = 0m/s

distance, s = 5cm or 0.05m

Using, v${}^2$ = u${}^2$ + 2as

0 = 75${}^2$ + 2a(0.05)

a = 562.5m/s${}^2$

$ Force = mass \times acceleration $

$ = 0.02 \times 562.5 $

= 11.25N