You are driving to the grocery store at 20 . You are 110 from an intersection wh

Question

You are driving to the grocery store at 20 . You are 110 from an intersection when the traffic light turns red. Assume that your reaction time is 0.50 and that your car brakes with constant acceleration. a.)How far are you from the intersection when you begin to apply the brakes? Express your answer to two significant figures and include the appropriate units. b.)What acceleration will bring you to rest right at the intersection? Express your answer to two significant figures and include the appropriate units. c.)How long does it take you to stop after the light turns red? Express your answer to two significant figures and include the appropriate units.

Explanation / Answer

How far do you travel during the reaction time. d = Vt = 20 * .5 = 10 m Therefore, you were originally 110 m away so now you are 100 - 10 = 100 m away from the intersection when you apply the brakes. Find the time it would take to stop (where Vf = 0). a = (Vf - V0)/t = -V0/t d = V0*t + 1/2 at² d = V0*t + 1/2 (-V0/t)*t² d = V0*t + 1/2*-V0*t d = 1/2 V0*t t = 2d/V0 t = (2*100)/20 = 10 s What is the acceleration a = -V0/t = -20/10 = -2 m/s²

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