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  • 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?)
    英語人氣:395 ℃時(shí)間:2020-02-05 23:20:44
    優(yōu)質(zhì)解答
    這次橄欖球比賽中,體重188磅的J.K接到了一個(gè)touchdown 傳球(就是接球手接到傳球并且?guī)ndzone 并且觸地)傳球手是G.S,J.K為了接住這個(gè)球,跳過了endzone左前方的對(duì)方防守.在這個(gè)跳躍過程中,J.K首先放低了身子以便起跳.我們假設(shè)J.K在跳前蹲了下來,他的重心(肚子底下左右)大約比他平時(shí)站姿的重心低14英寸.并且假設(shè)他離地的時(shí)間是0.8秒(我理解hang time是懸在空中的時(shí)間,也就是離地時(shí)間).請(qǐng)問他起跳時(shí)受到地面的壓力是多大?(提示:首先計(jì)算他起跳時(shí)的速度.然后考慮如何從蹲著的姿勢達(dá)到這個(gè)速度.有沒有涉及到加速度?)
    指考慮垂直方向,因?yàn)樵诳罩兄皇盏紾力,且知道時(shí)間,所以起跳時(shí)的速度可以求得.
    初速度是0,距離是14英寸,可求得加速度.vt平方減v0平方等于2as
    然后這個(gè)加速度是188磅M,受到G力和地面向上壓力合力的作用產(chǎn)生的,所以可以先求合力,減掉重力.能不能詳細(xì)一點(diǎn),第一步用什么公式去求起跳時(shí)的速度
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