问题 计算题

在某中学举办的智力竞赛中,有一个叫做“保护鸡蛋”的竞赛项目。要求制作一个装置,让鸡蛋从两层楼的高度落到地面且不被摔坏。如果没有保护,鸡蛋最多只能从0.1 m的高度落到地面而不被摔坏。有一位同学设计了如图所示的一个装置来保护鸡蛋,用A、B两块较粗糙的夹板夹住鸡蛋,A夹板和B夹板与鸡蛋之间的摩擦力都为鸡蛋重力的5倍。现将该装置从距地面4 m的高处落下,装置着地时间短且保持竖直不被弹起。取g=10 m/s2,不考虑空气阻力,求:

(1)如果没有保护,鸡蛋直接撞击地面而不被摔坏,其速度最大不能超过多少?

(2)如果使用该装置,鸡蛋夹放的位置离装置下端的距离x至少为多少米?(保留三位有效数字)

(3)为保证该实验的成功,你认为在制作该装置时,应需注意些什么?或做些什么改进?

答案

解:(1)vmm/s=1.41 m/s

(2)2Ff-mg=ma,Ff=5mg,a=9g

v=m/s

hminm =0.43 m

(3)A、B夹板的选择应该注意选软硬适中的材料,这样既能提供足够的摩擦力而又不会把鸡蛋挤坏;鸡蛋下滑通道的下端可以垫一些海绵等材料

完形填空
完型填空。
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单项选择题