Question

A 7000 kg railroad car is rolling at 3.0 m/s when it collides with a stationary 4000 kg railroad car. As they collide the cars stick together and move down the track. With what velocity do the cars travel down the track?5.25 m/s1.91 m/s2.52 m/s3.0 m/s

Answer 1

Given:

The mass of the first railroad car is,

`m_1=7000\text{ kg}`

The initial speed of the first railroad car is,

`u_1=3.0\text{ m/s}`

The mass of the other railroad car is,

`m_2=4000\text{ kg}`

The initial speed of the second railroad car is,

`u_2=0`

As they collide the cars stick together and move down the track.

To find:

The velocity do the cars travel down the track

Step-by-step explanation:

The linear momentum before the collision is,

`\begin{gathered} m_1u_1+m_2u_2 \\ =7000*3.0+4000*0 \\ =21000\text{ kg.m/s} \end{gathered}`

If the velocity after the collision is 'v', the linear momentum is,

`\begin{gathered} (m_1+m_2)v \\ =(7000+4000)v \\ =11000v \end{gathered}`

According to the linear momentum conservation principle,

`\begin{gathered} 11000v=21000 \\ v=(21000)/(11000) \\ v=1.91\text{ m/s} \end{gathered}`

Hence, the required velocity with which the cars will travel is 1.91 m/s.