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Entering a Freeway

  1. Jun 25, 2006 #1
    Entering the Freeway. A car sits in an entrance ramp to a freeway, waiting for a break in the traffic. The driver sees a small gap between a van and an 18-wheel truck and accelerates with constant acceleration along the ramp and onto the freeway. The car starts from rest, moves in a straight line, and has a speed of 30 m/s (67 mi/h) when it reaches the end of the 115 m long ramp.

    Ok for the acceleration I got 3.91 m/s/s and got that it takes 7.61 s for the car to travel the length of the ramp, but I dont understand part C:

    (c) The traffic on the freeway is moving at a constant speed of 30 m/s. What distance does the traffic travel while the car is moving the length of the ramp?

    i got 117.4 m but idk
     
  2. jcsd
  3. Jun 25, 2006 #2

    Hootenanny

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    These are both correct, however I think you have induced a rounding error, the time should be 7.67s
    I'm afraid this is not correct. Don't forget the traffic is travelling at a constant velocity.
     
  4. Jun 25, 2006 #3
    what did u get then? cuz im totally lost like i knew what i was doing for the first 2 parts but not this part.
     
  5. Jun 25, 2006 #4

    Hootenanny

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    I'm not giving you the answer :tongue2: . Think about traveling at constant velocity. What is the equation for uniform velocity? How do you define velocity?
     
  6. Jun 25, 2006 #5
    x=v of x times t
     
  7. Jun 25, 2006 #6

    Hootenanny

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    Thats right, distance is equal to the product of velocity and time. Use it:wink:
     
  8. Jun 25, 2006 #7
    well i put 29.75 and it said its wrong and it was my last submission so oh well, apparently 7.61 times 3.91 doesnt work.
     
  9. Jun 25, 2006 #8

    Hootenanny

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    3.91 is the acceleration of the car travelling up the ramp not the velocity of the cars travelling on the freeway which would be 7.66 x 30 = 230m
     
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