5. You are driving to school at 20 m/s. You are 35m from the intersection when t

Question

5. You are driving to school at 20 m/s. You are 35m from the intersection when the traffic light turns red. Assume that your reaction time is 0.15 seconds and that your car breaks with a constant acceleration (a) How far are you from the intersection when you begin to apply the brake? (b) What acceleration will bring you to rest right at the intersection? (c) How long does it take you to stop from the instant the light turns red? (d) A car is 3.0m behind you when the light turns red. The car is moving at a constant speed of 15m/s and the driver has a reaction time of 0.2s and his car brakes with a constant acceleration of 4.9m/s^2 how far was the car behind you at the instant you come to stop at the intersection? (12 points).

Explanation / Answer

(a) speed=20, reaction time =.15seconds , distance travelled =20*.15= 3m, thus 35-3=32m far from intersection

(b)

Using the formula v2-u2=2as

0-20*20=2*a*32

(c) using the formula. S=ut+ 0.5at2

=> 32=20*t- 0.5*6.258t2

=> t=3.2seconds

(d) using the formula, S=ut+0.5at2

=> s=15*3.2-0.5*4.9*3.22

S=22.9=23m

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