Question

A bullet with a mass of 0.1 kg hits a stationary 9 kg mass. The bullet bounces back with a speed of 300 m/s, while the mass moves off with a speed of 8 m/s. What is the initial speed of the bullet?

Answer 1

Given data

*The given mass of the bullet is m = 0.1 kg

*The given stationary mass is M = 9 kg

*The initial speed of the stationary mass is u_2 = 0 m/s

*The bullet bounces back with a speed is v_1 = 300 m/s

*The stationary mass moves off with a speed is v_2 = 8 m/s

The formula for the initial speed of the bullet is given by the conservation of momentum as

`mu_1+Mu_2=mv_1+Mv_2`

Substitute the known values in the above expression as

`\begin{gathered} 0.1* u_1+9*0=0.1*300+9*8 \\ 0.1u_1=30+72_{}_{} \\ u_1=1020\text{ m/s} \end{gathered}`

Hence, the initial speed of the bullet is u_1 = 1020 m/s