## College Physics (4th Edition)

(a) The total work done on the stunt woman is $3445~J$ (b) The work done by gravity is $4961~J$ (c) The work done by air resistance is $-1516~J$ (d) The average force of air resistance is $187 ~N$
(a) We can find the stunt woman's change in kinetic energy: $\frac{1}{2}mv^2 = \frac{1}{2}(62.5~kg)(10.5~m/s)^2 = 3445~J$ The total work done on the stunt woman is $3445~J$ (b) We can find the work done by gravity: $W_g = mgh = (62.5~kg)(9.80~m/s^2)(8.10~m) = 4961~J$ The work done by gravity is $4961~J$ (c) We can find the work $W_a$ done by air resistance: $Work = 3445~J$ $W_a+W_g = 3445~J$ $W_a = 3445~J-W_g$ $W_a = 3445~J-4961~J$ $W_a = -1516~J$ The work done by air resistance is $-1516~J$ (d) We can use the magnitude of the work done by air resistance to find the average force of air resistance: $F~d = W_a$ $F = \frac{W_a}{d}$ $F = \frac{1516~J}{8.10~m}$ $F = 187~N$ The average force of air resistance is $187 ~N$.