Q. Sand is being dropped on a conveyor belt at the rate of M kg/s. The force necessary to keep the belt moving with a constant velocity of v m/s will be
A) Zero
B) Mv newton
C) 2 Mv newton
D) Mv/2 newton
Explanation
[Solution from source] Each second a mass M of sand must be brought from zero to speed v, so F = v(dm/dt) = Mv newton. The force is not zero: even at constant belt speed, the momentum of the system keeps increasing as sand is added. Answer (2).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.