A worker moves a crate at constant speed while delivering a fixed mechanical power
PHYSICS · Single correct · A Level · Physics · Mechanics and materials · Mechanics and materials
Problem
A worker moves a crate at constant speed v while delivering a fixed mechanical power P. Initially the applied force makes an angle θ1 with the direction of motion. The worker then lowers the handle so that the angle becomes θ2, where θ2<θ1, while keeping both P and v unchanged. How does the magnitude of the required force change?
(a) It increases because F is proportional to cosθ, which becomes larger when the handle is lowered.
(b) It remains the same because P=Fv and both P and v are fixed.
(c) There is not enough information because changing the angle also changes the normal force and friction.
(d) It decreases because the cosine of the angle increases.