Work done by gravity and air resistance at terminal velocity

[anondukie]

Kaplan's physics review textbook claims that the work done by air resistance and gravity is equal at terminal velocity. However, I'm inclined to believe that they've made an error.

For gravity, the angle theta between force and displacement is 0 degrees. However, for air resistance it is 180 degrees. Therefore, the signs should be different (cosine 0 = 1; cosine 180 = -1).

Have I overlooked something? They weren't referring only to magnitude as far as I can tell.

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[aalamruad]

It seems pretty clear that they're referring to magnitudes.

Good critical reading though; that kind of thorough analysis should bode well for your test performance (although you might want to try to be a bit more efficient in your reasoning, i.e. if force and displacement are in the same direction, work will be positive, and if force and displacement are in opposite directions, work will be negative. No need to calculate angles and cosines).

 

[anondukie]

Thank you for the succinct answer and the generous compliment! I appreciate it!