英语翻译

题目

英语翻译
Under which of the following conditions is the magnitude of the average velocity of a particle moving in one dimension smaller than the average speed over some time interval?A.A particle moves in the +x direction without reversing.B.A particle moves in the -x direction without reversing.C.A particle moves in the + x direction and then reverses the direction of its motion.D.There are no conditions for which this is true.

答案

在下列情况中,求问：相同时间内物体的平均速度小于平均速率的选项是（）
A.物体沿+x移动,不掉头
B.物体沿-x移动,不掉头
C.物体沿+x移动,然后掉头
D.上述都不对
选C.因为平均速度=位移/时间,平均速率=路程/时间.既然时间相同,那么不掉头的运动其|位移|=路程,而掉头运动,|位移|<路程,所以|平均速度|<平均速率.