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Stopping Distance + Reaction Time Problem -> Physics beginner

  1. Aug 5, 2009 #1
    Stopping Distance + Reaction Time Problem ---> Physics beginner

    1. The problem statement, all variables and given/known data
    A car is traveling at 80km/h, and brakes with a reaction time of .5 seconds. The car decelerates at 8m/s/s, determine the stopping distance of the car.


    2. Relevant equations

    - V1 = V0 + at
    - D = V0t + 1/2at2

    Where:
    V1 = Final Speed
    V0 = Initial Speed
    A = Acceleration
    T = Time
    D = Distance

    3. The attempt at a solution

    Distance Traveled before Braking:
    80km/h = 22.22m/s

    0.5 * 22.22m/s = 11.11 m

    Distance After Reaction:
    V1 = V0 + at
    0 = 22.22 - 8t
    t = 2.7775 seconds

    D = V0t + 1/2at2
    D = 22.22 * 2.7775 - [(8 * 2.77752)/2]
    D = 30.86m

    Total Stopping Distance = 11.11m + 30.86m
    = 41.97 m

    Notes
    I am only beginning to learn some basic concepts of physics in class, so I'm not entirely sure about the equations.

    My teacher has provided no answer sheet to the question, and I am finding it hard to grasp the method of solving the question without a step by step example from a similar question.

    I'd greatly appreciate it if anyone could let me know if I am right, or how to do it if I am wrong.

    Thanks :D
     
  2. jcsd
  3. Aug 5, 2009 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Re: Stopping Distance + Reaction Time Problem ---> Physics beginner

    Looks good to me--everything's correct.

    FYI, there's another kinematic equation that relates velocity and distance directly for accelerated motion. That would enable you to combine a few steps. See: Basic Equations of 1-D Kinematics
     
  4. Aug 5, 2009 #3
    Re: Stopping Distance + Reaction Time Problem ---> Physics beginner

    Thank you for the help and additional formulas !
    Now I'll be able to do my other sums :D
     
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