This problem comes with a diagram so I have it at this link http://viewmorepics.myspace.com/index.cfm?fuseaction=viewImage&friendID=21023924&imageID=1274314408 It is problem number 3. I think that the work contributed by tension is zero since the force of tension is perpendicular to the motion of the pendulum in this case. Air resistance is negative since it is acting against the motion. What is the work contributed by the force of gravity. The answer key says that it is positive for part a and negative for part b, but why?