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Catching up

  1. Oct 25, 2005 #1
    Hi, ive got a big probllem:

    When you are 20m away from your bus it begins accelerating a 3m/s/s (from rest). What constant velocity should you run at to catch the bus.

    HELP!!!!!!!!!!!!!!!
    Please!!!!!!!!!!
    jason
     
  2. jcsd
  3. Oct 25, 2005 #2
    theres i big chance no one will help you unless you show an attempt
     
  4. Oct 25, 2005 #3

    Tom Mattson

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    Yep, you have to show that you've made an attempt.
     
  5. Oct 25, 2005 #4
    thats the think I have no idea where to begin

    The fruit of my labors is:
    me:
    Vi=?
    Vf=?
    t=?
    a=0
    d=to bus


    bus:
    Vi=0
    Vf=?
    t=?
    a=3m/s^2
    d=to bus
    This enough? because otherwise i am sol
     
    Last edited: Oct 25, 2005
  6. Oct 25, 2005 #5
    Try drawing two pictures; the first showing the initial conditions, and the second showing the final conditions when you've caught the bus.

    Once you've drawn the pictures, make sure you listed all your knowns.

    List your kinematics formulas so you can see what you have to work with.

    And don't forget to note your initial and final position.

    Try choosing your initial position as zero, which would make the initial position of the bus 20 m.
     
  7. Oct 25, 2005 #6
    Re:

    i have drawn a picture, listed my formulas( no idea which 1 to use though)
     
  8. Oct 25, 2005 #7

    Tom Mattson

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    You have yet to make use of that 20m in the problem statement. Let the motion be along the x-axis.

    Can you fill in the following information?

    Runner: xi=?
    Bus: xi=?
     
  9. Oct 25, 2005 #8
    ive been working more but all i have still is:thats the think I have no idea where to begin

    me:
    Vi=?
    Vf=Vi (constant)
    t=?
    a=0
    d=to bus-20


    bus:
    Vi=0
    Vf=?
    t=?
    a=3m/s^2
    d=to me+20
     
  10. Oct 25, 2005 #9

    Tom Mattson

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    In order to answer my question, you need to choose an origin for the coordinate system. Let's just put the runner's initial position at the origin, and let the bus sit to the right of the runner.

    Now can you fill in those values?
     
  11. Oct 25, 2005 #10
    me:
    Vi=?
    Vf=Vi (constant)
    t=?
    a=0
    d=distance run


    bus:
    Vi=0
    Vf=?
    t=?
    a=3m/s^2
    d=to run-20
     
  12. Oct 25, 2005 #11

    Tom Mattson

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    What I am asking you to do is assign an x-coordinate to both the runner and the bus initially. Do you know what a coordinate on a graph is?
     
  13. Oct 25, 2005 #12
    x would be distance and y would be time right?
     
  14. Oct 26, 2005 #13

    Tom Mattson

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    In the usual notation, x is distance and t is time. So if you have motion in 1 dimension, and we say that the motion is along the x-axis, and we say that the runner starts at the origin and that the bus starts out 20 meters to the right of the runner, then can you please tell me what the initial x-coordinate of both the runner and the bus are?

    We're happy to help with homework, but you have to work with us.
     
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