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拿火車運行作比較火車運行2000米用時20秒,平均速度是100米每秒,同時速度就約等於100米(因為位移和路程的區別,一個是有方向的,另一個沒有,所以速度約等於平均速度),速率是沒有方向的比如火車向東行駛的速度是100米/…
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