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How long it takes for a car to catch a truck

  1. Jun 1, 2012 #1
    1. The problem statement, all variables and given/known data
    A car traveling 91 km/h is 200m behind a truck traveling 81 km/h . How long will it take the car to reach the truck?

    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Jun 1, 2012 #2

    SammyS

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    Hello Pioneer98. Welcome to PF !

    What have you tried?

    Where are you stuck?
     
  4. Jun 1, 2012 #3
    I'm actually not even sure where to start. My professor gave us four kinematic equations to memorize and use. I know how to use those, but the things he went over in class are totally different from the online homework.
     
  5. Jun 1, 2012 #4

    HallsofIvy

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    Motion is always relative. The car is traveling at 10 km/hr faster than the truck. How long will it take to cover 200 m?
     
  6. Jun 1, 2012 #5
    20 seconds?
     
  7. Jun 1, 2012 #6

    SammyS

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    That would be true if car were traveling 10 m/s faster than the truck. Units matter !

    Convert 10 km/hr to m/s .
     
  8. Jun 1, 2012 #7
    10,000 m/hr, 2 7/9 m/s, so it takes 72 seconds for the car to reach the truck. Thanks for the help guys!!
     
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