# How much energy is dissipated as heat via friction?

1. Sep 12, 2011

### dangish

2. Hubert drags a 55 kg box over a rough surface of a dock with a constant force of 100N acting at an angle of 15 degrees to the horizontal. The box moves in a straight line for a distance of 6m. Friction acts at an opposite direction to the block and it is 75N. Calculate the work done to move the box? How much energy is dissipated as heat via friction? What is the final velocity of the box?

Ok so i started W=Fd

Would the force be the forces in the x direction? ie: 100cos15 - 75N ?

Which would give W = (100cos15 - 75) x 6 = 129.6Joules ??

Would that also be the energy dissipated as heat?

If so I could then use that to find the final velocity with E=1/2mv^2

2. Sep 12, 2011

### PhanthomJay

Re: Work/energy

There are forces in the x and y direction, but you are only intersted in the x direction for this problem, since the forces in the y direction do not do any work. you have correctly calculated the net force in the x direction.
yes, that is the net (or total) work done by all forces.
the problem asks for the energy dissipated as heat by the friction force.
Use what to find the final velocity (please clarify)?

3. Sep 12, 2011

### dangish

Re: Work/energy

So to find the energy dissipated by friction I should go W= 75 x 6 ??

4. Sep 12, 2011

### PhanthomJay

Re: Work/energy

Yes!

5. Sep 12, 2011

### dangish

Re: Work/energy

Then what about the final velocity? I know I have to use E=1/2mv^2

But It doesn't seem right to use the energy dissipated by the friction force

6. Sep 12, 2011

### PhanthomJay

Re: Work/energy

You are correct in that it doesn't seem right to just use the dissipated energy from friction, so instead, use the work-energy theorem to solve for the final KE.

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