Guide me through this plz.

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.
(Points : 1)
1.5 m/s

2.0 m/s

6.5 m/s

0.0011 m/s

Answer 1

momentum before = momentum after

1300 * 2 + 400 * 0 = 1700 v

v = 1300 * 2 / 1700

v = 1.5 m/s

Answer 2

Thank You :)

Answer 3

You are welcome.