Question

When the front of a 5.0 m long bus traveling at a constant speed of 20 m/s is 55 m away from an intersection, the traffic light turns yellow. It will take 3.0 s before the traffic light turns red. The driver’s reaction time is 0.25 s. The bus can accelerate up to 2.0 m/s2 or slow down at a maximum rate of 4.3 m/s2. The intersection is 22.0 m wide. Should the driver step on the brakes or on the gas pedal?

Answer 1

d = (V^2-Vo^2)/2a=(0-(20^2)/-8.6=46.51 m
= Stopping distance.

d = 55+22+5 = 82 m. = Distance through
intersection.

d = Vo*t + 0.5a*t^2 =
20*(3-0.25) + 0.5*2*(3-0.25)^2=62.6 m.

Therefore, the driver must step on the
brakes; because he or she cannot drive
the required 82 meters in 2.75 s.