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Constant Velocity (Finding when 2 objects will intersect)

  1. Aug 21, 2011 #1
    1. The problem statement, all variables and given/known data
    "Jim leaves at noon and drives east on I-10 at 60mph, Jenny leaves from the same location at 1:30PM, but travels at 70mph. When and where will Jenny catch up to Jim?"


    2. Relevant equations
    None.


    3. The attempt at a solution
    When doing a similar problem in class, we used substitution/elimination to solve. Basically, I just can't seem to set it up into an equation for time and distance.
     
  2. jcsd
  3. Aug 21, 2011 #2

    gneill

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    Staff: Mentor

    What formulas are you attempting to use to calculate their positions?
     
  4. Aug 21, 2011 #3
    Its a simple set of linear equations.

    Figure out 2 equations,
    1)The distance Jimmy is from the origin
    2) The distance Jenny is from the origin.

    Equate and you'll get your answer.
     
  5. Aug 21, 2011 #4
    Hmm.

    Ok, so would it be something like this?

    y=70x+1:30
    y=60x+12:00
     
    Last edited: Aug 21, 2011
  6. Aug 21, 2011 #5

    gneill

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    Staff: Mentor

    Define your variables. What does y represent? What does x represent? What are "1:30" and "12:00" supposed to mean in an equation? What units are attached to each of the quantities? Can you add "12:00" to "60x" and have it make sense?

    Think of the clock times as representing moments when you might start or stop a separate stopwatch which can start at zero. That way you won't have to deal with the inconvenience of hours of the day that have no direct relevance to the problem.

    In you classwork you must have been introduced to some formula that relates total distance to initial distance, velocity, and time traveled. What is it?
     
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