Question

A freight car moves along a frictionless level railroad track at constant speed. The freight car is open on top. A large load of coalis suddenly dumped into the car. What happens to the speed of the freight car?Select one:O A. Cannot be determined from the information given.O B. Becomes zeroO C. DecreasesO D. IncreasesO E. Remains the same

Answer 1

From the law of conservation of momentum, the momentum of a system should always remain constant.

And momentum is given as the product of mass and velocity of an object.

When a load of coal is dumped into the car, the mass of the system increase. Therefore, in order to for the momentum to remain constant, the velocity of the car should decrease.

Thus, the correct answer is option C.