Question

Car A (1200kg) travels at 15 m/s hits car B (initially at rest) from behind. Immediately after the collision,car B moves forward at 15m/s and car A is at rest. What is the mass of car B?

Answer 1

Given

Mass of car A, m=1200 kg

Speed of car A, u=15 m/s

Speed of car B, u'=0

After collision,

Speed of car A, v=0

Speed of car B, v'=15m/s

To find

Mass of the car B

Explanation

Let the mass of B be m'

By conservation of momentum

$\begin{gathered} mu+m^{\prime}u^{\prime}=mv+m^{\prime}v^{\prime} \\ \Rightarrow1200\times15+m^{\prime}\times0=1200\times0+m^{\prime}\times15 \\ \Rightarrow m^{\prime}=1200\text{ kg} \end{gathered}$

Conclusion

The mass of B is 1200 kg