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January 26, 2015

January 26, 2015

Posted by **george** on Monday, February 4, 2013 at 8:33am.

a.) if she hits the brakes, how far will she travel before stopping?

b.) if she hits the gas instead, how far will she travel before the light turns red?

c.) should she try to stop or should she speed up to cross the intersection before the light turns red?

- physics -
**Jennifer**, Tuesday, February 5, 2013 at 8:04pmuse

x = x0 + v0*t + 1/2*a*t^2

v = v0 + a*t

where x is position, x0 is initial position, v0 is initial speed, a is acceleration/deceleration, t is time, and v is speed as a function of time

a) 56 - 6.2*t^2 = 0

Solve for t, the time it takes for the speed to go to zero. The distance traveled in this time is then 1/2*6.2*t^2

b) 56 + a*4.2 = 70

Solve for a, the acceleration

Then calculated the distance she travels (I would assume that she stops accelerating after she hits 70 km/hr

So for the first 4.2 seconds, she travels

x1 = 56*t + 1/2*a*4.2^2

and then she travels an additional distance:

x2 = 70*(20-4.2)

for a total distance of x1 + x2

c) Evaluate where she will be in part a) and b) with respect to the traffic lights and decide what she should do

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