做功(题目是英语的)..能帮的麻烦进来解答

(1) Work is defined as W = F.S cos(theta) since theta = 0 (Ok,you could argue that it could as well be 180,but it is just not commonly seen.),hence W = 375 * 10m/s *1s * 1 = 3750 J
(2).Since the water skier is moving at uniform speed,his kinetic energy is K = 0.5*m.V^2,now his mass cannot change (Unless he is burning his muscles and fat :P) and hence his kinetic energy gain is 0.
For your additional question,my suggestion is as follows:from Newton's second law we have:
F_net = ma,right?Now a = 0 m/s^2 (uniform speed) and hence F_net = 0 N,is it OK?
But we see from the question that there have already been a tension of 375N from the string,how could it be?
If you draw a free-body diagram,you could find out that aside from the tension,there are other forces acting on the skier,e.g.friction from the water,the portion of the skier's gravitational force on his moving direction and etc.These force,as you could deduce from the formula in the first question,do a negative work on the skier,and the NET effect of all these forces is that their work cancels out each other.I believe in your physics book,the author would stress that the change in the kinetic energy results from ALL forces acting on that object.
Hope that clarifies.

(A)w=fs =375*10*1=3750J
(B获得的动能为0，因为滑车做匀速运动，速度不变 动能不变

1.375*10=3750牛顿米
2. 0 speed and mass of the water skier do not change.
kinetic energy =1/2mv^2,
可以转化其他形式的能，如内能，热能，势能。不一定就是动能