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Homework Help: Angular Velocity & Angular Acceleration

  1. Jul 11, 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 +19.5 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 +11.5 revolutions.

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

    (b) What is the angular acceleration of each wheel?

    2. Relevant equations

    avg ang. v=ang. x/t

    avg ang. a=change in ang. v / t

    3. The attempt at a solution

    I plugged in and got...

    delta theta=11.5 x 2pi=72.26 radians


    72.26rad/(t) = 19.5

    and so t=3.7 or 3.706 or 3.71 and all those are wrong... I dont know what i did wrong.
  2. jcsd
  3. Jul 11, 2007 #2


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    Science Advisor
    Homework Helper

    You are treating this as problem with uniform angular velocity. Clearly that's not true since the bike is slowing down. You need the analog of x(t)=x0+v0*t+(1/2)*a*t^2. Remember linear motion?
  4. Jul 11, 2007 #3
    thanks i got the problem right after i typed it though =)
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