Constant force but angle is increased, what happens to work

[Frankenstein19]

Homework Statement

A box is dragged a distance d across the floor by a force F which makes an angle theta with the horizontal. If the magnitude of the force is held constant but the angle theta is increased, does the work remain the same, increase, decrease, or first increase and then decrease?

Homework Equations

The Attempt at a Solution

Ok so I know what the graph of cosine looks like, which initially (well if we start from zero, anyway) goes down and then up and then down and so on. But I don't have an option that says that. The correct answer is that it decreases. If I make a table on my calculator with it being in degree mode, I can see that cosine gets smaller and smaller as the angle increases, however, when it's in radian mode it goes from -1 to 1. I don't understand why work decreases as the angle is increased.

 

[TSny]

If I make a table on my calculator with it being in degree mode, I can see that cosine gets smaller and smaller as the angle increases, however, when it's in radian mode it goes from -1 to 1. I don't understand why work decreases as the angle is increased.

I don't understand how you are getting the cosine to increase from -1 to 1 as the angle θ in the work formula increases. Note that θ always lies between 0 and 180 degrees; that is, between 0 and $\pi$ radians. So, what happens to the cosine function as θ goes from 0 radians to $\pi$ radians?