How to find the length of the track?

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Can someone please explain to me how to do question 5? Thanks!

1 Answer
Dec 26, 2017
  1. First driver. He starts with initial velocity =0.
    His velocity after accelerating for 3s can be found from the kinematic expression

    v=u+at
    :.v_1=0+16xx3=48ms^-1.
    Distance moved in these 3s can be calculated by the kinematic expression
    s=ut+1/2at^2
    :.s_13=0xx3+1/2xx16xx3^2=72m
    Crash occurs after 9-3=6s when he stops accelerating.
    Distance moved during these 6s can be found from the expression
    s=vt
    s_16=48xx6=288m
    Total distance moved by first driver=72+288=360m

  2. Second driver. He too starts with initial velocity =0.
    His velocity after accelerating for 5s

    v_2=0+20xx5=100ms^-1.
    Distance moved in these 5s
    s_25=0xx5+1/2xx20xx5^2=250m
    Crash occurs after 9-5=4s when he stops accelerating.
    Distance moved during these 4s
    s_24=100xx4=400m
    Total distance moved by second driver=250+400=650m
    Length of track= Sum of distances moved by both drivers
    =288+650=938m