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I have tried to answer the problem correctly, and I have found similar (and even an identical) problem in my textbook, yet I still can't seem to yield the correct answer with this specific problem.

The example problem in my textbook: A crate is hauled 8m up a ramp under a constant force of 200 N applied at an angle of 25 degrees to the ramp. Find the work done. W = F * D cos(25) = (200)(8)cos(25) = 1450J.

Can anyone give me any advice on how to solve it?

A woman exerts a horizontal force of 4 pounds on a box as she pushes it up a ramp that is 5 feet long and inclined at an angle of 30 degrees above the horizontal.

Find the work done on the box.

I would think that the work would simply be (4)(5)cos(30), but that is not the correct answer.

(I've figured out how to accept answers now, so I'll accept the most helpful answer.)

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closed as off-topic by Qmechanic Nov 3 '13 at 2:25

This question appears to be off-topic. The users who voted to close gave this specific reason:

  • "Homework-like questions should ask about a specific physics concept and show some effort to work through the problem. We want our questions to be useful to the broader community, and to future users. See our meta site for more guidance on how to edit your question to make it better" – Qmechanic
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Note that in one case the angle is given with respect to the ramp and in the other with respect to the horizontal. Compare to the definition of work. – dmckee Jan 31 '11 at 19:57
Also, note that the question says 'work done on the box' not work supplied to the box by the 'man/woman'. Though this is a distinction that question writers get lazy about. – Jerry Schirmer Jan 31 '11 at 23:26
up vote 0 down vote accepted

Your answer "(4)(5) cos(30)" with units of "foot-lbs" is correct for the problem as you've stated it, however there are other forces on the box. You might try including gravity.

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I asked my professor. (4)(5)cos(30) is correct when the calculation uses degrees, but it was incorrect because it uses radians. The answer is technically (4)(5)cos(pi/6). Thank you all for the help.

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