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Homework Help: Dynamics- Angular Impulse and Momentum Problem

  1. Dec 19, 2012 #1
    1. The problem statement, all variables and given/known data
    The 30-kg reel is mounted on the 20-kg cart. If the cable wrapped around the inner hub of the reel, with radius 150mm, is subjected to a force of P=50 N, determine the velocity of the cart and the angular velocity of the reel when t=4 sec . The radius of gyration of the reel about its center of mass O is kO = 250 mm. Neglect the size of the small wheels.
    Attached is a picture

    2. Relevant equations
    IG1+Σ [itex]\int[/itex]MGdt=IG2

    3. The attempt at a solution
    I=mk2=1.875 kg/m2
    So my impulse equation solves down to:
    I end up with 2 variables and 1 equation. What is my missing equation, or how do I relate ω2 and v2?

    Attached Files:

  2. jcsd
  3. Dec 26, 2012 #2

    rude man

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    Homework Helper
    Gold Member

    Sorry no one has responded thus far.

    Not my specialty, but I would base my computations on two interpretations:

    1. Irrespective of the motion of the cart, there is a constant torque τ applied to the reel, with resulting angular acceleration, that torque being τ = P*r1 where r1 = radius of inner hub. Thus θ'' = τ/I and you have already computed I, hopefully correctly.

    2. The only force applied to the cart + wheel assembly is P. So P = Mx'' for the assembly where M = total assembly mass (50kg).

    If these observations hold then the problem is actually quite straightforward. I think they do. I notice that your "impulse equation" has inconsistent dimensions within it.
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