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Determine the time it take for the car and the truck to meet

  1. Jul 12, 2005 #1
    a car starts from rest at a point 300m from a truch that is moving at a constant rate of 30m/s toward the car. IF the car accelerates at .8m/s2, determine the time it take for the car and the truck to meet.
    s=300
    This is what I did
    Car:
    Vi = 0, a = .8
    Vf^2=2as = Vf=21.9

    Vf=at
    21.9/.8 = 27.38
    t=27.38sec

    Truck:
    S=(V/2)t
    S=(15)t
    300/15 = 20
    t=20

    They meet after (27.38 -20) = 7.38 seconds.

    The answer given is 8.94seconds. Not sure what I am doing wrong?????
     
  2. jcsd
  3. Jul 12, 2005 #2

    James R

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    You assumed the truck meets the car at 300 m. It doesn't, because the truck is moving towards the car.
     
  4. Jul 12, 2005 #3

    Pyrrhus

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    You will need to set up your equation such as the car will cover a distance x, which will be the distance the truck meets the car, but the truck will cover a distance x+300.
     
  5. Jul 13, 2005 #4
    dont you mean 300 - x
     
  6. Jul 13, 2005 #5

    Pyrrhus

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    Depends on where you put your coordinate system, i put the origin on the car.
     
  7. Jul 13, 2005 #6
    Thank you all for your help - Arden
     
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