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Homework Help: Circular Motion of bicycle

  1. Apr 14, 2010 #1
    1. The problem statement, all variables and given/known data
    A rock stuck in the tread of a 53.0 cm diameter bicycle wheel has a tangential speed of 3.50 m/s. When the brakes are applied, the rock's tangential deceleration is 1.20 m/s^2.

    X.) What is the magnitudes of the rock's angular velocity (omega) when t = 1.60s?
    Y.) What is the magnitudes of the rock's angular acceleration (alpha) when t = 1.60s?
    Z.) At what time is the magnitude of the rock's acceleration equal to g? (9.8 m/s^2)

    2. Relevant equations
    v = r(omega)
    a = r(omega)^2
    Vf = Vi + a[tangental](dt)
    D[omega] = alpha(dt)
    omega^2 = omega0^2 + 2(alpha)(dtheta)

    3. The attempt at a solution
    X.) r = 0.265m, a[tangental] = -1.2, Vi = 3.5, dt = 1.6
    Vf = 3.5 + (-1.2)(1.6) = 1.58
    omega = 1.58/0.265 = 5.962 {incorrect apparently}

    Y.) omega1 = 3.5/.265 = 13.208
    (13.208 - 5.962) = alpha(1.6)
    alpha = 4.528 {incorrect, but expected because X is incorrect}
     
  2. jcsd
  3. Apr 14, 2010 #2

    vela

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    That's correct. Maybe you're not entering it in the right units or with the correct number of significant figures.
    That's correct too, although you took a roundabout way of calculating it.
     
  4. Apr 14, 2010 #3
    its asking for omega in rad/sec & alpha in rad/sec^2... would that affect my answers any?
     
  5. Apr 14, 2010 #4

    vela

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    Nope. Radians is the natural unit for measuring angles.
     
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