Pendulum question...?

Question

As a simple pendulum swings back and forth, the forces acting on the suspended object are the force of gravity, the tension in the supporting cord, and air resistance.

a) Which of these forces, if any, does no work on the pendulum?
b) Which of these forces does negative work at all times during the pendulum's motion?
(c) Describe the work done by the force of gravity while the pendulum is swinging.

Answer 1

A. The tension in the cord is along a radius of the weight's path directed through the weight's CM, so it is always perpendicular to the velocity which is tangential to the same point. Thus it does no work on the weight.
B. Air resistance is always opposite to the weight's motion so it does negative work on the weight.
C. Gravity does both positive (on the downswing) and negative (on the upswing) work during the course of a cycle. If the amplitude is constant, the net energy exchange over each cycle is zero.

Answer 2

ummmm, yes? I mean, those are the forces acting on the pendulum. There could also be some friction between surfaces due to the rope's rubbing on the object (not phrased well)...