A team of skydivers jumps from a plane and holds hands to fo

来源：学生作业帮编辑：神马作文网作业帮分类：物理作业时间：2024/11/06 12:45:01

A team of skydivers jumps from a plane and holds hands to form a flower-like design.As the skydivers begin their free fall,their velocity increases and their
(A)acceleration increases
(B)acceleration decreases
(C)acceleration is constant
(D)acceleration is zero
(E)air resistance is reduced
跳伞运动员在开始free fall之前做的是什么运动（就是form a flower-like design时）?还有,这个free fall到底是个什么概念?跟自由落体是不是一回事?
其实答案是B

（Sorry,是偶看错了,这不是自由落体,是有阻力的落体运动.）
刚开始下落加速速度最大(a=g),速度由零增加,空气阻力变大（f=kv,k是常数）,加速度a=(mg-kv)/m自然减少.然而重力终归大于阻力,速度越来越大,最后阻力达到与重力相等时,a=0,他下降就变为匀速运动了（此速度称为收尾速度）
有兴趣的话,也可以写写其运动方程：
v=（mg/k)(1-e^(-kt/m)),其中e是自然对数,k是阻力系数
a=ge^(-kt/m)
下图是加速度随时间变化的图像,可见其由g变小,趋向于0.

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