A flatbed railcar of mass 800 kg rolls without friction along a straight
PHYSICS · Multi-part · ISC · Physics · Laws of Motion · Laws of Motion
Problem
A flatbed railcar of mass 800 kg rolls without friction along a straight, level track at a constant speed of 3.0 m/s. Beginning at t = 0, sand falls vertically from a stationary hopper onto the car at a steady rate of 5.0 kg/s for 10 s. Air resistance is negligible, and the sand does not bounce upon landing.
(a) For the system consisting only of the railcar, is horizontal momentum conserved during the 10 s while sand is being added? Explain clearly.
(b) For the system consisting of the railcar plus all sand that is in the air or on the car at a given instant, is horizontal momentum conserved during the same interval? Justify your answer.
(c) Qualitatively describe how the speed of the railcar changes while sand is being added, and explain your reasoning in terms of impulse.