WHAT IS THE WORK DONE THAT IS DISSIPATED AS HEAT?

[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

 

[Doc Al]

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

 

[jinx007]

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

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

 

[Doc Al]

So some converts to kinetic energy and potential enegy..

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

No, your answer is not correct. But you'll get there.

 

[jinx007]

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

No, your answer is not correct. But you'll get there.

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

 

[Doc Al]

So p.e is 20 kN x 12

Good!

What about the kinetic energy..?? no speed...what should i do..

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

 

[jinx007]

Good!

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

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..?

 

[Doc Al]

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..?

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.

 

[jinx007]

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.

Awww..but what is the answer..?..

 

[Doc Al]

Awww..but what is the answer..?..

See my hint in post #2. You know the total work done. And you know how much went to PE and KE. What's left?