An emergency lift of mass carries passengers up a mine shaft
PHYSICS · Multi-part · CBSE · Physics · Work, Energy and Power · Work, Energy and Power
Problem
An emergency lift of mass 800kg carries passengers up a mine shaft. The lift is pulled upward 30m at constant speed by a cable connected to a motor that supplies mechanical power at a steady rate of 22kW for the entire ascent. Neglect air resistance.
(a) Calculate the change in gravitational potential energy of the lift-plus-passengers system during the 30m ascent.
(b) Determine the total mechanical work done on the lift by the cable during the ascent.
(c) Using the motor’s power output, compute the minimum possible time required for the 30m ascent if all of the mechanical energy delivered by the motor went into increasing potential energy.
(d) The actual ascent takes 12s. Compare this time with your answer to part (c) and discuss what the comparison reveals about additional forms of energy transfer that must be occurring.