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Homework Help: Car collision using multiple formulas

  1. Jan 26, 2012 #1
    1. The problem statement, all variables and given/known data
    I'm not sure where to begin with this problem

    A car is travelling West at 35mph. 45 feet in front of this car is an intersection , and another car is about to turn in front of the westbound car. Could the car safely complete the left hand turn , or would the westbound car have to come to a complete stop to avoid striking the other vehicle. I have read that 2-3 seconds between cars is an adequate amount of time for reactions , and what if the westbound car just let off the gas. How would I be able to account for a light rain as well?
    I'm not exactly sure where to start with this problem , but any assistance would be appreciated.

    2. Relevant equations
    Vf^2 = Vo^2 -2ad

    3. The attempt at a solution
    I know this is really basic , but I'm not sure where to turn exactly...
  2. jcsd
  3. Jan 27, 2012 #2


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    Homework Helper

    You need to estimate - or be told - how long the turning car will take to complete its turn.

    You could consider how long it takes the moving car to cover the 45 feet at a speed of 35mph.

    If those two times are equal, then the turn should be safely completed.

    You could consider if the car can even stop before the intersection. What is the braking distance for a car travelling at 35 mph? certainly if there was light rain the braking distance would be greater.
    Who knows, stopping might not be an option if it is raining - or even if it is fine.

    Unless you have access to reasonable braking rates and acceleration rates [the turning car has to accelerate] you will most probably assume unrealistic values for at least one of them.

    EDIT: btw 0.4 seconds is deemed a reasonable reaction rate for an alert driver. Reaction time is the time before you begin doing what ever you decide to do.
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