大师作文网老师说题里的信息如果不全可以自己假设一个,比如速度不知道就可以假设这个人的速度是50.
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老师说题里的信息如果不全可以自己假设一个,比如速度不知道就可以假设这个人的速度是50.
Anakin and Sebulba are pod-racing on the plante Tatooine.The race includes a sharp (90 degrees) left turn around a cliff that Anakin is approaching and Sebulla has already completed.Sebulba's speed is 500mph.Anakin's radar tells him that the distance between him and Sebulba is decreasing at a reat of 120mph.How fast is Anakin going when he is 8 miles due north of the intersection point ans Sebulba is 6 miles due east of it?
Anakin and Sebulba are pod-racing on the plante Tatooine.The race includes a sharp (90 degrees) left turn around a cliff that Anakin is approaching and Sebulla has already completed.Sebulba's speed is 500mph.Anakin's radar tells him that the distance between him and Sebulba is decreasing at a reat of 120mph.How fast is Anakin going when he is 8 miles due north of the intersection point ans Sebulba is 6 miles due east of it?
Choose the coordinates this way: the intersection as the origin, east is +x, north +y
When Anakin (A) is 8 miles north of the intersection, let the time be 0 hour, and his speed is v mph
At the moment of t hours: AS = 8 - vt miles; Sebulba (S) is 6 + 500t miles from origin.
l = sqrt[(8 - vt)^2 + (6 + 500t)^2]
dl/dt = [2(8 - vt)(-v) + 2(6 + 500t)*500]/{2sqrt[(8 - vt)^2 + (6 + 500t)^2]}
= [500(6 + 500t) - v(8 - vt)]/sqrt[(8 - vt)^2 + (6 + 500t)^2]
t = 0, dl/dt = -120 = (500*6 - 8v)/sqrt(8^2 + 6^2) = (3000 - 8v)/10
v = 525 mph
When Anakin (A) is 8 miles north of the intersection, let the time be 0 hour, and his speed is v mph
At the moment of t hours: AS = 8 - vt miles; Sebulba (S) is 6 + 500t miles from origin.
l = sqrt[(8 - vt)^2 + (6 + 500t)^2]
dl/dt = [2(8 - vt)(-v) + 2(6 + 500t)*500]/{2sqrt[(8 - vt)^2 + (6 + 500t)^2]}
= [500(6 + 500t) - v(8 - vt)]/sqrt[(8 - vt)^2 + (6 + 500t)^2]
t = 0, dl/dt = -120 = (500*6 - 8v)/sqrt(8^2 + 6^2) = (3000 - 8v)/10
v = 525 mph
老师说题里的信息如果不全可以自己假设一个,比如速度不知道就可以假设这个人的速度是50.
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