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A radius vector

  1. Apr 13, 2010 #1
    1. The problem statement, all variables and given/known data
    A radius vector of a particle varies with time t as r=at(1-[tex]\alpha[/tex]t) where "a" is a constant vector [tex]\alpha[/tex] is a positive factor.
    Find:
    a) velocity "v" and the acceleration [tex]\omega[/tex] as function of time;
    b) the time interval [tex]\Delta[/tex]t taken by the particle to return to the initial points and the distance "s" covered during this time.

    I have solved a) and have problem with b)


    2. Relevant equations

    r=at(1-[tex]\alpha[/tex]t)
    v=a(1-2[tex]\alpha[/tex]t)
    [tex]\omega[/tex]=-2[tex]\alpha[/tex]

    3. The attempt at a solution
    To find time I should divide r/v? I don't understand that. The result is: t=1/[tex]\alpha[/tex].
    Now how find distance? Substitute founded time to equation as r?
    Looking for some help, my phisical english isn't so good , because come from Poland. Thx
     
  2. jcsd
  3. Apr 13, 2010 #2

    tiny-tim

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    Welcome to PF!

    Hi phisics99! Welcome to PF! :smile:

    (have an alpha: α and an omega: ω :wink:)
    (btw, your ω is missing an α :wink:)

    To find time, just use the original equation, r = at(1 - αt) …

    r = 0 at t = 0 and at t = … ? :smile:

    (and then use one of the standard constant acceleration equations to get distance)
     
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