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Homework Help: Dynamics help: variable acceleration and angular velocity

  1. Feb 20, 2013 #1
    I have to do these 2 problems for homework, but I can't figure them out. Any help would be appreciated.

    1. The motorcycle is traveling at 1m/s when it is at A(the origin). If the speed is then increased at [itex] \dot{V} = .1 m/s^2[/itex], determine its speed and acceleration at the instant t = 5 seconds. The motorcycle is following the curve [itex]y = 0.5 x^2[/itex].

    2. Rod OA rotates counterclockwise with a constant angular velocity of θ = 6 rad/s. Through mechanical means collar B moves along the rod with a speed of [itex]r = 4 t^2 m/s[/itex], where t is in seconds. If r = 0 when t = 0, determine the magnitudes of velocity and acceleration of the collar when t = 0.75 sec.

    This is the link to the image for question 2:
    Last edited: Feb 20, 2013
  2. jcsd
  3. Feb 20, 2013 #2
    For question 1, start with the Kinematic Equations, specifically v = u + at
  4. Feb 20, 2013 #3
    so using v = u + at:

    v = 1m/s + .1(5)
    v = 1.5 m/s

    now I need a. i believe i need to find radial and tangential a?
    so i have a = vdot
    so a_r = .1 m/s^2
    but how do I get the acceleration that is based on the curve y = .5x^2?
  5. Feb 20, 2013 #4


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    I don't think you can use that here. The rate of increase of speed is constant, but that's not the same as acceleration as strictly defined. Acceleration is a vector, or a component of a vector in a consistent direction.
    medynamics, try to write down some equations relating dx/dt, dy/dt etc.

    It's not a good idea to put two unrelated problems in the same thread.
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