A single 1,300 kg cargo train car is rolling along a train track at 2.0 m/s when 400 kg of coal is dropped vertically into it. What is its velocity right afterward? Assume a closed system.

1.5 m/s

2.0 m/s

6.5 m/s

0.0011 m/s

Question

A single 1,300 kg cargo train car is rolling along a train track at 2.0 m/s when 400 kg of coal is dropped vertically into it. What is its velocity right afterward? Assume a closed system.

1.5 m/s

2.0 m/s

6.5 m/s

0.0011 m/s

jamesj · Answer

Use Conservation of Momentum.  The momentum of the train before the coal added is equal to the momentum after the coal is added.  See what to do now?

anonymous · Answer

not really :(

anonymous · Answer

The definition of momentum is$$\vec p = m \vec v$$So if momentum before the coal is dropped must equal the momentum before this event occurs. $$\vec p_i = \vec p_f$$Hopefully you can see what to do now!