physics

a motorist traveling at 18m/s approaches traffic lights. when he is 30m from the stop line they turn red .it takes 0.7s before he can react by appling the breakes. the car slow down at a rate of 4.6m/s^2 how far from the stop line will he come to rest and on which side of it?

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  1. distance traveled: .7*18+distance braking
    distance braking: Vf^2=Vi^2+2ad or d=18^2/(2*4.6)=35.2m
    distance trveled= .7*18+35.2m

  2. nice but it is not cear

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  3. A distance travelled before applying a brake =0.7*18=12.6m
    A distance travelled after applying brakes=vi2/2a,where as vf=0,s=sqrt18/2*4.6=35.2m
    The total the motorist travel=12.6+35.2=47.8m
    Therefore the distance between the stop line and the motorist stopped (the total motorist traveled) =47.8m-30m=17.8m

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