The elevator E has a mass of 3000 kg when fully loaded and is connected as shown to a counterweight W of mass 1000 kg. Determine the power in kilowatts delivered by the motor: (a) when the elevator is moving down at a constant speed of 3 m/s, (b) when it has an upward velocity of 3 m/s and a deceleration of 0.5 m/s².

Question

G1 Physics · Accepted Answer

Write force balance for the elevator and counterweight and use motor power P=T·v with sign according to whether the motor absorbs or supplies energy. For downward constant 3 m/s motion, the motor power is -30 kW; for upward 3 m/s with 0.5 m/s² downward acceleration, it is 19.5 kW. Hence A.