Question

A bullet of mass $50g$ is moving with a velocity of $500m/s$. It penetrates $10cm$ into a still target and comes to rest. Calculate:

1. the kinetic energy possessed by the bullet, and
2. the average retarding force offered by the target

Answer 1

Step 1: Given

Mass of the bullet, $m=50g=0.05kg$

Velocity of the bullet, $v=500m/s$

Distance penetrated by the bullet, $s=10cm=0.1m$

Step 2: Calculate the kinetic energy

$$\begin{gathered} KE=\frac{1}{2}m{v}^2 \\ =\frac{1}{2}\times 0.05\times {\left(500\right)}^2 \\ =6250kg-m^2/s^2 \\ =6250J \end{gathered}$$

Step 3: Determine the average retarding force

Work done is given by, $W=Force\times Dis\tan ce$

In this situation, Work done = Resistance force x distance

$$\begin{gathered} W=KE=6250=F\times 0.1 \\ \Rightarrow F=62500N \end{gathered}$$

Therefore,

1. the kinetic energy possessed by the bullet is $6250N$
2. the average retarding force offered by the target is $62500N$