Question
An elevator has a mass of 341 kg It moves up 18 m in 22.3 s and uses 7.92times 10^4 Jof electricity. Calculate the power output of this energy transformation. (4)
Solution
4.2
(305 Votes)
Filbert
Master · Tutor for 5 years
Answer
1. **Calculate the work done against gravity:**Work (W) = force (F) x distance (d)The force here is the weight of the elevator, which is its mass times the acceleration due to gravity (g = 9.8 m/s²).F = m * g = 341 kg * 9.8 m/s² = 3341.8 NW = 3341.8 N * 18 m = 60152.4 JThis is the work done *against* gravity. The elevator's motor does more work than this because it also has to overcome friction and accelerate the elevator.2. **Calculate the total work done by the motor:**The problem states the elevator uses 7.92 x 10⁴ J of electricity. We assume this energy is completely converted to mechanical work by the motor (100% efficiency, which is a simplification). Therefore, the total work done by the motor is 79200 J.3. **Calculate the power output:**Power (P) is the rate at which work is done. It's calculated as work divided by time.P = W / t = 79200 J / 22.3 s = 3551.57 W4. **Express the answer with the correct significant figures:**The given values have three significant figures, so the answer should also have three significant figures.P ≈ 3550 W or 3.55 x 10³ W