Power and Energy of a motor problem

  • Thread starter majormuss
  • Start date
  • #1
124
4

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

Homework Equations



P=Wd/t= Fd/t= mad/t

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'.
 

Answers and Replies

  • #2
lewando
Homework Helper
Gold Member
1,349
135
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.
 
  • #3
393
0

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

Homework Equations



P=Wd/t= Fd/t= mad/t

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'.
Fv should work as well as wd/t, because d/t = v. To find the force, draw a force body diagram. What forces are acting on the 400kg object? Remember, force does not equal acceleration. A NET force equals an acceleration.
 

Related Threads on Power and Energy of a motor problem

  • Last Post
Replies
3
Views
359
  • Last Post
Replies
1
Views
897
  • Last Post
Replies
3
Views
3K
  • Last Post
Replies
7
Views
2K
Replies
3
Views
6K
Replies
1
Views
4K
Replies
7
Views
560
Replies
3
Views
1K
  • Last Post
Replies
0
Views
1K
Replies
10
Views
1K
Top