physics hw, uniformly accelerating questions?

Question

A person driving her car at 60 km/h approaches an intersection just as the traffic light turns yellow. She knows that the yellow light lasts only 2.0 s before turning to red, and she is 30 m away from the near side of the intersection (Fig. 2-29). Should she try to stop, or should she make a run for it? The intersection is 15 m wide. Her car's maximum deceleration is -6.2 m/s2, whereas it can accelerate from 60 km/h to 70 km/h in 3.0 s. Ignore the length of her car and her reaction time.
If she hits the brakes, how far will she travel before stopping?

________m

If she hits the gas instead, how far will she travel before the light turns red?

________m.

Sorry there is no picture!!! :(

Answer 1

a.) How far before stopping?
v(avg) = (v(i) + v(f)/2 = (60 + 0)/2 = 30.0m/s
a = (v(f) - v(i))/t
t = (v(f) - v(i))/a
t = -60/-6.2 = 9.6774s
D = vt
D = 30.0(9.6774) = 290.3m [way past the intersection]

b.)
Acceleration: [assume uniform acceleration from 60km/h to 70km/h]
a = (v(f) - v(i))/t
a = (70 - 60)/3
s = s(zero) + v(zero)t + (1/2)at^2
s = 60(2.0) + (1/2)(3.33)
s = 126.67m > 30 + 15 [way past the intersection in 2 sec.]