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Homework Help: What is the angular acceleration of each wheel?

  1. Nov 23, 2007 #1
    1. The problem statement, all variables and given/known data

    A person is riding a bicycle, and its wheels have an angular velocity of +20.0 rad/s.

    Then, the brakes are applied and the bike is brought to a uniform stop.

    During braking, the angular displacement of each wheel is +10.0 revolutions.

    (a) How much time does it take for the bike to come to rest?
    in seconds

    (b) What is the angular acceleration of each wheel?
    in rad/s2

    2. Relevant equations

    3. The attempt at a solution

    what is the symbol of a revolution. Can i use a kinematic equation for this.
  2. jcsd
  3. Nov 23, 2007 #2


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    Homework Helper

    hm..angular displacement.[itex]\theta[/itex] is related to angular velocity,[itex]\omega[/itex]
    by the equation:


    where t is time
  4. Nov 23, 2007 #3
    okay, so if i manipulate the formula to look like t = theta / w

    then the time is .5 seconds, however, that is not correct?
  5. Nov 23, 2007 #4
    a)for the first one use kinematics formula


    so we have


    [tex]\alpha d\theta=\omega d\omega[/tex]

  6. Nov 23, 2007 #5
    for the first one, 1 second isn't the anwer and i'm not sure why

    i used 10 rev = (+20 - 0)/2 t

    so 1 second??

    also, for the second one

    20^2 = 400

    so 400/2

    and that is not correct either.

    i'm not sure what i did wrong.
    Last edited: Nov 23, 2007
  7. Nov 24, 2007 #6
    You're mixing revolutions with radians, you'll have to convert units to one or the other.
  8. Nov 24, 2007 #7
    thanks, that fixed it, i didn't realise that 1 revolution is actually convert to 2 * pi radians

    i got the answers: 6.3 seconds and -3.17 rad/s^2
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