A person driving her car at 55 km/h approaches an intersection just as the traff

Question

A person driving her car at 55 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. The intersection is 15 m wide. Her car's maximum deceleration is -5.0 m/s2, whereas it can accelerate from 55 km/h to 70 km/h in 4.5 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
Should she try to stop, or should she speed up to cross the intersection before the light turns red?

stop/ speed up   

Explanation / Answer

55 km/h = 15.28 m/s

from the kinematic equation v^2-u^2 = 2as

here v = 0

15.28^2 = 2*5*s

s = 23.34 m

b) from the equation v = u+at

(70-55)*5/18 = a*4.5

a = 0.93 m/s^2

s = ut+1/2at^2 = 15.28*2+1/2*0.93*2^2 = 32.29 m

she can not cross the street in 2 sec.so, she could apply breaks it is better

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