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#