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Kinematic Question -- Car braking to avoid hitting a fox

  1. Apr 27, 2016 #1
    1. The problem statement, all variables and given/known data

    Andrew is driving his van to deliver groceries in Elmvale. As he travels along Hwy 92, a fox stops on the road. Andrew is travelling at 75 km/h and is 42 m away from the fox when he applies his brakes. It takes him 3.4 s to stop.

    a) How far did Andrew travel before stopping?

    b) Did Andrew hit the fox? Explain your answer by including a calculation.

    c) If a typical van is 4.2 m in length, how many van lengths did it take Andrew to stop?

    2. Relevant equations
    Δd = v2+v1/2 (Δt)

    3. The attempt at a solution

    v1 = 75 km/h
    convert 75 km/h to m/s = 20.8 m/s

    Δd = 42 m

    Δt = 3.4 s

    a) Δd = v2+v1/2 (Δt)
    Δd = (0 m/s + 20.8 m/s) /2 x (3.4s)
    Δd = 35.36 m

    Andrew travelled 35.36 m before stopping.

    b) 42 m - 35.36 m = 6.64 m
    Andrew stoped 6.64 m in front of the fox and therefore did not hit it.

    c) 35.36 m / 4.2 m = 8.4 van lengths
    It took approximately 8 van lengths for Andrew to stop.

    Please look over this and tell me if it is correct. Thanks :)
  2. jcsd
  3. Apr 27, 2016 #2


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    It all looks good.

    The formula Δd = v2+v1/2 (Δt) should be written with parentheses in the numerator as Δd = (v2+v1)/2 (Δt) in order to indicate the proper order of operations.
    Last edited: Apr 27, 2016
  4. Apr 27, 2016 #3
    Ok, thanks for checking it out :)
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