PHYSICS · Multi-part · A Level · Physics · Mechanics and materials · Mechanics and materials
Problem
Two construction hoists, A and B, are used to lift identical loads of roofing material from the ground to the top of a 25 m tall building. Hoist A is driven by a motor that can supply a maximum average output of 6.0 kW, while Hoist B’s motor can supply 9.0 kW.
Assume that each load is raised at constant speed and that mechanical energy losses are negligible.
(a) Describe qualitatively which hoist can complete the lift in a shorter time and explain your reasoning using appropriate physical relationships.
(b) Derive an algebraic expression for the ratio tBtA of the time required by Hoist A to the time required by Hoist B.
(c) If each load has a mass of 350kg, calculate the numeric value of the ratio from part (b) and interpret its meaning in the context of the scenario.