# Work, energy and power

1. Aug 29, 2010

### jinx007

A constant force of 9 kN parallel to an inclined plane, moves a body of weight 20 kN through a distance of 40m along a plane at a constant speed. The body gains 12 m height..

HOW MUCH WORK IS DISSIPATED AS HEAT?

A/ 120 KJ

B/ 240 KJ

C/ 360 KJ

D/ 600 KJ

So workdone = f x d

but i am a bit confuse as the question say the heat dissipated

so i think that the work done = 20 kN X 12 = 240 KN (heat dissipated) answer

However the work done is 9 KN X 40 = 360 KJ

AM I ON THE RIGHT TRACK ????? HELP BY THE WAY ACCORDING TO ME THE ANSWER IS B

2. Aug 29, 2010

### Staff: Mentor

You know the total work done by the force. Where does that energy go? Some goes to heat, but where does the rest go?

3. Aug 29, 2010

### jinx007

So some converts to kinetic energy and potential enegy..please just tell me whether i am on the right track and if the answer is correct... thanks in advance

4. Aug 29, 2010

### Staff: Mentor

Good. In this case, how much energy goes to KE? How much to PE?

5. Sep 9, 2010

### jinx007

So p.e is 20 kN x 12
What about the kinetic energy..?? no speed...what should i do...

6. Sep 9, 2010

### Staff: Mentor

Good!
You are told that the speed is constant. So how much of the total work goes into KE?

7. Sep 10, 2010

### jinx007

So i think that its the work done of moving the object to the top this is equal to the kinetic energy..!!! i am right..???

8. Sep 10, 2010

### Staff: Mentor

No. Since the speed of the object--and thus its kinetic energy--doesn't change, none of the work is transformed into kinetic energy. There is no change in kinetic energy.

9. Sep 10, 2010