The head of a grass string trimmer has m = g of cord wound in a light, cylindrical spool with inside diameter d1 = cm and outside diameter d2 = cm as shown in Figure P10.58. The cord has a linear density of p = g/m. A single strand of the cord extends l = cm from the outer edge of the spool.
(a) When switched on, the trimmer speeds up from 0 to w1 = rev/min in t = s. What average power is delivered to the head by the trimmer motor while it is accelerating?
(b) When the trimmer is cutting grass, it spins at w2 = rev/min and the grass exerts an average tangential force of f = N on the outer end of the cord, which is still at a radial distance of l = cm from the outer edge of the spool. What is the power delivered to the head under load?

r1 =
r2 =
b =