问题补充:
答案:
(a) Assuming that each stroke is a perfect half circle,the distance of each stroke is L=½πD=0.5x3.14x1.8=2.83 m.
Therefore,the work done in each stroke is F x L=260N x 2.83m=734.8 J.
(b) In each stroke,the upward and downward force is not useful in pulling him along.
The useful work done in each stroke is F x D=260N x 1.8m=468 J.
Time of each stroke 60/110=0.545 s.
Therefore,the useful power is 468 / 0.545 = 858.0 W.