# Power and Energy of a motor problem

## Homework Statement

What is the average power developed by a motor
as it lifts a 400.-kilogram mass at constant speed
through a vertical distance of 10.0 meters in
8.0 seconds?
(1) 320 W (3) 4,900 W
(2) 500 W (4) 32,000 W

## The Attempt at a Solution

How does the fact that acceleration is 0 change the way I should approach this question. The question says acceleration is constant.
On the other hand I tried using this formula.... P=Fv..... but because I dont know acceleration, I can't find 'F'.

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lewando
Homework Helper
Gold Member
The correct equation for power is: P=W/t

What is work? (W=Fd)
What is force? (F = ma)

In this problem, there are 2 accelerations to consider: (1) The problem says the speed is constant so the acceleration of the mass as it travels through space is 0. (2) assuming that this motor is operating near the surface of the Earth, the acceleration due to Earth's gravity is acting on the mass.

## Homework Statement

What is the average power developed by a motor
as it lifts a 400.-kilogram mass at constant speed
through a vertical distance of 10.0 meters in
8.0 seconds?
(1) 320 W (3) 4,900 W
(2) 500 W (4) 32,000 W