Opent top freight train with coal

[12boone]

Question 3 text A freight car moves along a frictionless level railroad track at constant speed. The car is open on top. A large load of coal is suddenly dumped into the car. What happens to the velocity of the car?
Question 3 answers
It increases.
It remains the same.
It decreases. <-----
cannot be determined from the information given

 

[Rake-MC]

Looks good to me. Use conservation of momentum to confirm.

$$m_1v_1 = m_2v_2$$

m₂ is greater than m₁ therefore v has to decrease.