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在解某些物理习题时,根据定律、公式列出方程后,有时会发现未知数的个数多于方程的个数,或所要求的物理量在方程中根本不出现,解答就较为围难.对这类问题往往可以利用常识列出辅助方程,从而顺利解题.如下面举的几例. 例1.质量为m的物块放在水平面上,物体与地面的摩擦系数为μ.与水平面成30°角,大小为1/2mg的力F作用在物体上,第一次是拉,第二次是推(分别如图1a、图1b所示).设第一次拉使物体移动距离s,已知在拉和推的过程中,克服摩擦力所做的功相同.求物体第二次移动的距离和μ的范围。
In solving some physical exercises, after listing the equations according to laws and formulas, it is sometimes found that the number of unknowns is more than the number of equations, or the required physical quantity does not appear in the equation at all, and the solution is more difficult. This type of problem can often use common sense to list auxiliary equations for smooth problem solving. Examples are given below. Example 1. A block of mass m is placed on a horizontal surface and the friction coefficient between the object and the ground is μ. At a 30° angle, a force F of a size of 1/2 mg acts on the object. The first time it is pulled and the second time it is pushed (as shown in Figure 1a and Figure 1b, respectively). Let the first pull make the object move a distance s It is known that in the process of pulling and pushing, the work done by overcoming friction is the same. The distance and μ range of the object are required to move for the second time.