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Physics Kinematics Problem

  1. Dec 23, 2008 #1
    1. The problem statement, all variables and given/known data
    A car travelling @ 20 m/s pulls out to pass a truck travelling @ 18m/s. The car accelerates for 2.0m/s^2 for 4s and maintains new velocity.
    (c.) If the car was originally 8.0 m behind the truck when it pulled out to pass, how far in front of the truck is the car 10.0 s later?


    I did the first two parts, but I got stumpted at the third (above mentioned part c.)


    3. The attempt at a solution
    I'm 100% sure what I did is wrong. I don't really know where to use the 8.0 m
    d = Vi(t) + 1/2 a t^2
    = 80m + 100m
    = 180 m???

    HELP! Thanks in advance. Just trying to go over all physics chapters before the finals. Ntn better to do in the winter hols lolz. Trying to get on the honour roll for the first time ever. Thanks in advance again!!
     
  2. jcsd
  3. Dec 23, 2008 #2

    jgens

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    Well, start by calculating the total distance travelled by each car.
     
  4. Dec 23, 2008 #3
    Using which time?
     
  5. Dec 23, 2008 #4

    jgens

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    Well, since no other information is given about the truck, assume it travels at constant velocity for 10 seconds. All that's left then is to calculate the distance travelled by the car which can be done in two seperate parts: the first when the car is accelerating and the second when it travels at constant velocity for the rest of the time.
     
  6. Dec 23, 2008 #5
    okay then,
    d(truck)= 18m/s x 10s
    = 180m

    d(car) = vit + 1/2 at^2

    Using 4s, d = 96m
    Using 10s, d =300m

    Where do I go from here to get my final answer?
     
  7. Dec 23, 2008 #6

    jgens

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    I agree with your distance travelled for the first four seconds but how did you get 300 for the total distance travelled? The car only accelerates for four seconds not ten. The car travels at constant velocity for six seconds.
     
  8. Dec 23, 2008 #7
    Right, right, thanks. So now, how do I find the distance between the car and the truck 10s later? Could you give me the steps? I suspect that I should add the 4s distance and the truck distance... Or is the answer just the 4s distance of the car?
     
  9. Dec 23, 2008 #8

    jgens

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    Ok, so what is the total distance travelled by the car and what is the total distance travelled by the truck? Use these distances along with the 8 meters to determine how far ahead the car now is.
     
  10. Dec 23, 2008 #9
    Alrighty then, thanks much
     
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