OG11-黃DS79 (已查過無詳解計算....)

Kath1985 · 发表于 2010-3-25 20:53:03

While on a straight road, car X and car Y are traveling at different constant rates.
If car X is now 1 mile ahead of car Y, how many minutes from now will car X be 2 miles ahead of car Y?
i) Car X is traveling at 50 miles per hour and car Y is traveling at 40 miles per hour.
ii) Three minutes ago car X was 1/2 mile ahead of car Y.
答案為D
想問
1我有疑問是黃色部分的意思是 ?
2.能不能請牛牛將條件1和2的計算式子寫出來呢 ? OG的解釋看不懂...........

感謝了

rainrooney · 发表于 2010-3-25 21:05:14

delta s(0)=s(x,0)-s(y,0)=1, delta s(t)=s(x,t)-s(y,t)=2, t=?
(I) v(x)=50; v(y)=40
delta V=v(x)-v(y)=10
delta s(t) - delta s(0)=2-1=1=delta v * t=10*t, t=0.1
(II) delta s(-3min)=1/2
delta v(constant)=delta s/ delta t=[delta s(0) - delta s(-3min)] /3min = [delta s(t) - delta s(0)]/t
1/6min=1/t, t=6min

Kath1985 · 发表于 2010-3-29 21:16:36

黃色部分的意思是 ?

OG11-黃DS79 (已查過無詳解計算....)

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