An elevator takes a 70 kg person from street level to the top of a 400 m sky-scraper in 4 minutes. The mass of the elevator is 500 kg.
a] At what rate is the elevator plus the person gaining potential energy?
b] What power is the elevator plus the person experiencing as it climbs?
c] The motor driving the lift has an efficiency of only 25%. At what rate is the motor working as the lift is going up?
How can the elevator calculation be incorporated with the person?
How can the efficiency affect the calculation for the work of the motor? [/B]
The Attempt at a Solution
mgh = (70kg)(9.8m/s^2)(400m)
Work = Force*Displacement
rate of Work = Power
Efficiency = Workout/Workin*100%
0.25 * (400m*500kg*9.8m/s^2)/240s
Power = Work/Time
4 minutes = 240 s