Question

Consider a 42,000 kg train car travelling at 10 m/s toward another train car. After the two cars collide, theycouple together and move along at 6 m/s. What is the mass of the second train car? (28,000 kg) Please show work

Answer 1

Given data:

* The mass of the first train car is,

`m_1=42000\text{ kg}`

* The initial velocity of the first train car is,

`u_1_{}=10\text{ m/s}`

* The velocity of the couple train car is,

`v=6\text{ m/s}`

Solution:

By the law of conservation of momentum,

`p_i=p_f`

where p_i is the initial momentum of net system, and p_f is the final momentum of the net system,

`m_1u_1+m_2u_2=(m_1+m_2)v`

where m_2 is the mass of the second train car, and u_2 is the initial velocity of the second train car,

`\begin{gathered} 42000*10+0=(42000+m_2)*6 \\ 420000=252000+m_2*6 \\ 6m_2=168000 \\ m_2=(168000)/(6) \\ m_2=28000\text{ kg} \end{gathered}`

Thus, the mass of the second train car is 28000 kg.