# Homework Help - Calculus III / Physics / Work-Force Problem #2

I'm in a similar scenario as with my other question. 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.

-
Do you have the actual numerical answer? Your method of computation seems ok. I wonder if it is a problem of units. –  Willie Wong Jan 31 '11 at 18:39
consider posting on Physics Exchange also. –  ja72 Jan 31 '11 at 18:44
How about exchanging cos with sin. Does $4 5 \cos(30^\circ)$ yield the correct result? (if the ramp is not inclined at all, no work should be done) –  Fabian Mar 2 '11 at 22:37
First of all dear @Math Student as you say applied force is 4 pounds which (though i seldom work in such units) means that fore applied is 4 * g (acceleration due to gravity). –  HarshCurious Mar 15 '11 at 4:44
In Imperial units, the base unit is pounds as a unit of force, so you should not multiply by g. We have slugs as a unit of mass, and also lbm to confuse things. –  Ross Millikan Mar 15 '11 at 5:09

As Fabian said in a comment, the $\cos$ should be $\sin$

-
Another source of error, is the sin() function, in case it expects a number in radians and you supply it in degrees.
You answer in lbs $\times$ ft is not in Joules. Multiply by 1.35581795 to convert to Joules.