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Homework Help: Angular speed people walking problem

  1. Nov 17, 2008 #1
    1. The problem statement, all variables and given/known data
    Two people start at the same place and walk around a circular lake in opposite directions. One has an angular speed of 1.7*10-3 rad/s, while the other has an angular speed of 3.4*10-3 rad/s. How long will it be before they meet?

    2. Relevant equations
    w=[tex]\theta[/tex]/Delta t
    *v=vo+at ~ w=wo+[tex]\omega[/tex]t
    *v2=vo2+2ax ~ w2=wo2+2[tex]\omega[/tex][tex]\theta[/tex]
    *x=vot+(1/2)at2 ~ [tex]\theta[/tex]=wot+(1/2)at2

    the ones with * means i changed it to what the problem is about. means the same thing just different letters so you wont get confused i guess.

    3. The attempt at a solution
    how do you set that up in the problem i gave because theres no value that is for rad/s. or is that omega? you plug that in there? because the seconds are supposed to be squared. im so lost. i just learned this today too. its great. please help!

    thank you!
    Last edited: Nov 17, 2008
  2. jcsd
  3. Nov 17, 2008 #2
    This is similar to your bullet problem. You have a speed and a distance but you need a time. Do you know the total distance? Do you know the total speed?
  4. Nov 17, 2008 #3


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    How many radians are they apart when they start? 1 revolution is how many radians?

    How fast are the walking toward each other? How many radians per second are the closing on each other?

    Distance/speed = time doesn't it?
  5. Nov 17, 2008 #4
    i dont know the distance or speed. all the information i had i gave. it was word for word from the problem. theres no extra reference or anything.
  6. Nov 17, 2008 #5
    Your angular distance is all the way around the circle, or 2 pi radians. The total speed is the speed of the two walkers added together. They are starting back to back walking away from each other around a circular lake.

    Maybe it will help you to draw a diagram of the problem...
  7. Nov 17, 2008 #6


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    Gee it looks like you are given their angular rates of walking about the lake.

    And you know how many radians there are in one revolution.

    You have all you need.
  8. Nov 17, 2008 #7
    i know the rates and there like 6.28 radians in one revolution. but what equation am i supposed to use?
  9. Nov 17, 2008 #8
    Do you know what each one means? Which one makes sense given the problem you are trying to solve and the information provided?
  10. Nov 17, 2008 #9


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    ω * t = θ = 2π

    You know what their rate of walking toward each other is.
  11. Nov 17, 2008 #10
    no i dont know what they mean. i just started learning this today and i have no idea what im doing.
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