A driver in a car is traveling on a horizontal road at constant speed of 30 m/s

Question

A driver in a car is traveling on a horizontal road at constant speed of 30 m/s and observes a traffic light 100 m away changing from green to yellow. The drivers takes 1.30 s in order to react and apply the brakes. The car stops at the traffic light. Draw and label a diagram representing the initial physical situation. Determine the distance from the traffic light that the driver is at the instant that the brakes are applied. Determine the constant braking acceleration needed to stop at the traffic light. Determine the time interval from when the driver observes the traffic fight change from green to yellow until the car stops at the traffic fight. Carefully draw and label a graph of the velocity (vertical axis) versus the time (horizontal axis) for the time interval when the driver first observes the traffic light until the car stops. Explain how the graph describes the motion.

Explanation / Answer

B)

d = 100 - ( v * t)

d = 100 - ( 30 * 1.3)

d = 61 m

C)

from the equation

v^2 - u^2 = 2 * a * d

0 - 30^2 = 2 * a * 61

a = - 7. 37 m/s

D)

from v = u + a * t

0 = 30 + (-7.37 *t)

t = 4.07 s

total time T = 4.07 + 1.3

T = 5.37 s

E)

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