please help!! :( These are the only two questions I can\'t figureout on my test

Question

please help!! :( These are the only two questions I can't figureout on my test review.

A car starts from rest at a stop sign. It accelerates at 4.0m/s2 for 6 seconds, coastsfor 3 s, and then slows down at a rateof 3.0 m/s2 for the next stop sign. How far apart arethe stop signs?


The minimum stopping distance for a car traveling at a speed of 30m/s is 60 m, including the distance traveled during the driver'sreaction time of 0.50 s. What is the minimum stopping distance forthe same car traveling at a speed of 40 m/s?

Explanation / Answer

Q1)          duringacceleration:          initialvelocity = 0         distancetravelled, S1 = (1/2) at 2 = (1/2) (4) (36) = 72 m         distancetravelled, S1 = (1/2) at 2 = (1/2) (4) (36) = 72 m       final velocity = at = 4( 6 ) = 24 m/s       during deceleration:         initial velocity =24 m/s       distance travelled, S2=  V 2 - U 2 / 2 a = (0 - 576) / ( 2) ( -3) = 96 m       distance between two stopsigns, d = S1 + S2 = 72 + 96 = 168 m Q2)       Stopping distance, S V 2       ( S2 / S1) = ( V2 / V1)2 = (40/30) 2 = 16 /9         S2 = (16/9) 60 =106.67 m       ( S2 / S1) = ( V2 / V1)2 = (40/30) 2 = 16 /9         S2 = (16/9) 60 =106.67 m

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