The mechanical efficiency of elevator a is higher than that of elevator B. they respectively lift objects of the same mass to the same height at a constant speed A. A lift does less total work B. B lift does less total work c. a lift does less useful work D. B lift does more useful work

The mechanical efficiency of elevator a is higher than that of elevator B. they respectively lift objects of the same mass to the same height at a constant speed A. A lift does less total work B. B lift does less total work c. a lift does less useful work D. B lift does more useful work

A. If the active work is the same, the mechanical efficiency of a is high, according to the formula η = w useful w total, the total work of the motor is less, correct; B, if the active work is the same, the mechanical efficiency of B is low, according to the formula η = w useful w total, the total work of the motor is more, wrong; CD, lifting objects of the same quality to the same height, according to w useful = GH = MGH, the active work is the same, wrong; so select a