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1) We have a box with mass m being dragged over a rough horizontal surface by a constant force F at an angle @ above the horizontal; it travels d meters and there is a kinetic frictional coefficient of u. What is the work done on the block?

2) What is the work done by the force of friction.

3) Determine it's final speed assuming it's initial velocity was 0.

Attempted Answer:

1)

Fx = F cos @ - uN = m a_x (1)

Fy = F sin @ + N - m g = 0 (2)

From (2) we have N = m g - F sin @, substituting into (1) we have

F cos @ - u (m g - F sin @) = m a_x

Therefore, W = [ F cos @ - u (m g - F sin @)] d

But this is the wrong answer?!?!

2) I don't know how to set this up; what are we solving for?

3) If I can come up with the right answer for (1), I can determine the acceleration and determine it's final speed via one of the one-dimensional motion equations.

please help! :-)

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# Homework Help: Box dragged along resistant surface, work = ?

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