A team of skydivers jumps from a plane and holds hands to fo
来源:学生作业帮 编辑:作业帮 分类:物理作业 时间:2024/09/03 10:00:25
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
(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.
![](http://img.wesiedu.com/upload/9/dd/9dd1e8c34e72c76bf2e38db1f7c50144.jpg)
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.
![](http://img.wesiedu.com/upload/9/dd/9dd1e8c34e72c76bf2e38db1f7c50144.jpg)
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