[解題] 國三理化 直線運動
1.年級:國三
2.科目:理化
3.章節:
直線運動
4.題目:
一台車東西做直線運動 從原點靜止開始 以加速度4M/S^2 往東 然後
又以2M/S^2 向西 過了兩秒停止 共走150M 求總歷時多少??
5.想法:
我先設從靜止過了t秒 開始要以2M/S^2 向西 此時走了S
所以 S=0.5*4*t^2=2t^2 ---(1)
那此時V=4t 走了150-S 就回停止
故 0^2=(4t)^2-2*2*(150-S) 將16t^2 換成8S
0=8S-4(150-S) 得S=50
代回(1) t=5秒 所以總歷時=5+2=7秒
可是答案是5秒??? why?
麻煩一下 謝謝
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