- #1

- 3

- 0

## Homework Statement

**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?

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?

## Homework Equations

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