高中物理 做功(题目是英语的)..能帮的麻烦进来解答

来源：百度知道 编辑：UC知道 时间：2024/06/08 09:12:27
A water skier is pulled by a string and slides on an inclined platform at a uniform speed of 10 ms^-1. The tension in the string is 375N.Assume the tension is the string is parallel to the displacement of the skier.
(a)How much work has the tension done on the water skier for 1s?
(b)How much kinetic energy does the skier gain 1s?explain briefly.
在 题(b) 请详细解释一下...可以用中文... 还有一个问题就是 如果 力F 对一个物体 做功 ...那个物体的动能一定会起 增加或减少...因为做功的定义是 The amount of energy transferred in such process is called Work

(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 co