如图，某一物体沿两个半径为R的半圆弧由A运动到C，则它的位移和路程分别是
A．0，0
B．4 R、向下，πR
C．4πR向下、4R
D．4R向下，2πR
答案：D
题目分析：两个半径为R的半圆弧由A运动到C，位移为：从A到C的直线距离，即4R，方向向下，路程为运动轨迹的长度为：2πR。
故选D
点评：位移是位置的变化，路程是运动的轨迹；位移是矢量，路程是标量．位移的大小等于由初位置指向末位置有向线段的长度，与运动轨迹无关．路程是运动轨迹的长度。
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