1.一架車剎掣後,衝行了80m才停定.假設剎掣後,氣車受路面的摩擦力為10000N.氣車的質量為1000kg,,氣車剎掣前的速率為多少kmh^-1?
需要列明公式!!!!!
牛頓第二運動定律
2006-12-17 10:48 pm
回答 (2)
2006-12-17 11:15 pm
✔ 最佳答案
F = ma 10000 = (1000)a
a = 10 ms^-2
or a = -10 ms^-2 [-10 因為是減速，a的方向和v相反]
v^2 = u^2 + 2aS
0 = u^2 + 2(-10)(80)
u^2 = 160
u=40 ms^-1
2006-12-18 7:27 am
We can use the principle of work done , because the car finanlly stopped, the work done by the frictional force of the road is equal to the kinetic energy of the car .
F.S = 1/2mv^2
10000(80) = 1/2(1000)v^2 ,where v is the speed of the car just before started to brake
v = 40
F.S = 1/2mv^2
10000(80) = 1/2(1000)v^2 ,where v is the speed of the car just before started to brake
v = 40
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