A car is running along a straight road for 10 min. Its average velocity is 70 kmh-1 and its instantaneous velocity is 50kmh-1 at t=3 min. Which must be correct?
1. The distance travelled by the car is 1.17x10^4m
2The magnitude of the displacement is the same as distance travelled
3. The car acccelerates at some moments during the trip
ANS: 3 only
Why not the others? plz help with clear explanation for each statement THZ
Motion MC
2007-12-13 8:04 pm
回答 (1)
2007-12-13 9:10 pm
✔ 最佳答案
1 是不對的因為我們不知道在0-3 min 內架車的詳細速度情況﹐所以無可能只道架車行了幾多公里。
2 是不對的
一樣﹐因為我們不知道在0-3 min 內架車的詳細速度情況﹐所以無可能只道架車的位移(displacement)是不是等於距離(distance)例如架車可以一開始向後駛﹐到t=3 min 才以50kmh-1 向前駛﹐則位移是負數而距離是正數。
3是對的
因為在t=3 min 時速度是50kmh^-1﹐不等於70kmh^-1﹐所以(無論在t=3 min 平均時速是不是70kmh-1)在以後一定要有個時段加速或者減速才可令到10分鐘內的平均時速是70kmh-1
2007-12-13 13:11:05 補充：
只道應是知道
收錄日期: 2021-04-26 13:05:17
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20071213000051KK00917