解与机械效率有关的题,类型多、涉及的物理量多,同学们感到比较困难．怎样才能掌握解题方法,形成清晰的解题思路呢? 首先必须准确理解几个概念,会分辨总功、有用功、额外功．而且要注意两个易错点: 1．W有用用不一定等于Gh．①提升物体时,克服物体的重力做功,W有用=Gh．若物体浸没在液体中,只要拉力大小等于G-F浮,就可以把 Solve the problems related to mechanical efficiency, many types, many physical quantities involved, the students feel more difficult. How can we master the problem-solving method and form a clear problem-solving idea? First of all, we must accurately understand several concepts, and we will distinguish the total work, useful work, and extra work. And pay attention to two error-prone points: W useful is not necessarily equal to Gh. 1 When lifting an object, overcome the gravity of the object to do work, W = Gh. If the object is immersed in the liquid, as long as the pull force is equal to the G-F float,