这次橄榄球比赛中,体重188磅的J.K接到了一个touchdown 传球（就是接球手接到传球并且带endzone 并且触地）传球手是G.S,J.K为了接住这个球,跳过了endzone左前方的对方防守.在这个跳跃过程中,J.K首先放低了身子以便起跳.我们假设J.K在跳前蹲了下来,他的重心（肚子底下左右）大约比他平时站姿的重心低14英寸.并且假设他离地的时间是0.8秒（我理解hang time是悬在空中的时间,也就是离地时间）.请问他起跳时受到地面的压力是多大?（提示：首先计算他起跳时的速度.然后考虑如何从蹲着的姿势达到这个速度.有没有涉及到加速度?）
指考虑垂直方向,因为在空中只收到G力,且知道时间,所以起跳时的速度可以求得.
初速度是0,距离是14英寸,可求得加速度.vt平方减v0平方等于2as
然后这个加速度是188磅M,受到G力和地面向上压力合力的作用产生的,所以可以先求合力,减掉重力.能不能详细一点，第一步用什么公式去求起跳时的速度
At the scintillating game against the New England Patriots yesterday,Jeremy Kerley (188 lbs mass) caught a touchdown pas
At the scintillating game against the New England Patriots yesterday,Jeremy Kerley (188 lbs mass) caught a touchdown pass.To catch the ball thrown by Geno Smith he leaped above the defender at the front left corner of the end zone.In the process he first lowered his body to prepare to launch himself.Let’s assume that when he squatted down before he jumped,his center of mass (just below his belly button) was about 14 inches lower than his normal standing position.Assuming that his hang time was 0.8 s,what was the force he exerted on the ground when he jumped?(Hint:First calculate the initial velocity when he jumped up.Then,consider how that velocity was generated from the squat position.Was there an acceleration involved?)
英语人气：240 ℃时间：2020-02-05 23:20:44
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