A 3400 kg open railroad car coasts along with a constant speed of 7.50 m/s on a level track. Snow begins to fall vertically and fills the car at a rate of 5.10 kg/min.Ignoring friction with the tracks, what is the speed of the car after 85.0 min ?

Answer 1

After 85 min, 433.5 kg has been added to the railroad car. The momentum will stay the same because there is no friction (or so they say). The new mass of the car with snow in it is 3833.5 kg.

Use the law of conservation of momentum.

3400 * 7.50 = 3833.5 * Vfinal

Whoever dreamed up this problem is out of touch with the real world. There is no way a railroad car can go 85 minutes on a level track without friction. Friction will slow it down more than the falling snow that fills it.