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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

    and

    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

    Dick

    User Avatar
    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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