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## Homework Statement

A blue car pulls away from a red stop-light just after it has turned green with a constant acceleration of .5 m/s^2.

A green car arrives at the position of the stop-light 7 s after the light has turned green.

What is the lapse time of the blue car when the green car catches it if the green car maintains the slowest constant speed necessary to catch up to the blue car? Answer in units of s.

**2. Relevant questions**

I'm having trouble grasping how to find "the slowest constant speed necessary" I'm assuming I need to set up two equations and set them equal to each other, but I'm given no information about the green car!

## The Attempt at a Solution

Well, short of the green car I have it set up that for the blue car

Vi = 0 m/s

a = .5

t = 7 seconds

so

V = AT

V = 3.5 m/s when the green car gets to the stop light and the blue car has gone

x-xi = Vi * t + 1/2 A T^2 = 42.25 meters.

so if the blue car is going 3.5 m/s with .5 m/s^2 and it has an initial x component of 42.25 from the green car after 7 seconds, I need to find the time that the green car will catch up with the slowest possible speed..

I'm stuck I can't think of how to deal with this.

Do I assume the accleration on the green car is 0? Since it talks only about speed? Then I need to find a constant speed which will probably be quite high relative to the blue car where they intersect each other? How do I go about doing this?

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