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题目:水平地面上一质量m=500克的足球,离墙s=6米,墙高h=1.8米。要将球踢过墙头,运动员至少要对球做多少功?(g取10米/秒~2) 解:球被踢出后,做斜抛运动。球刚好飞越墙头,其运动轨迹有如附图所示的A、B、C三种情况。球飞起的角度不同,初速度的大小也就要不同。要使踢球时对球做功最少,就要使球获得的动能(即使球脱离人脚时的速度)最小。求这个极值,通常的方法过程复杂,容易出错。这里介绍一种简捷的巧妙的处理方法如下: 根据斜抛运动的规律,有
Title: A football with a mass of m=500 grams on the horizontal ground, s=6 meters away from the wall, and the wall height h=1.8 meters. To kick the ball over the wall, how much does the player have to do with the ball? (g takes 10m/s~2) Solution: After the ball is kicked out, it will do a diagonal movement. The ball just flew over the wall, and its movement trajectory was A, B, C as shown in the figure. Different angles of the ball fly, the size of the initial speed will also be different. To make the least work on the ball while playing, it is necessary to minimize the kinetic energy obtained by the ball (even if the ball is separated from the human foot). For this extreme value, the usual method is complicated and error-prone. Here is a brief and clever way to deal with it as follows: According to the law of slanting, there are