Question

A 20000kg railroad car is traveling at 5 m/s when it collided and coupled with a second, identical car at rest. What is the resulting speed of the combined cans?

Answer 1

We know that in a collision the momentum of the system is conserved, that is:

$p_i=p_f$

In this case, since the railroad cars coupled together and have the same mass we have:

$mv_1+mu_1=2mv$

Now, we know the initial velocity of the cars, one is traveling at 5 m/s and the other is at rest; plugging the values and solving for the final velocity we have:

$\begin{gathered} 20000(5)+20000(0)=2(20000)v \\ v=\frac{5(20000)}{2(20000)} \\ v=2.5 \end{gathered}$

Therefore, the velocity of the combined cars is 2.5 m/s