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Homework Help: Help-physics to get started

  1. Jan 4, 2004 #1
    An object of mass m is tied to a light string wound around a wheel that has a moment of inertia I and radius R. The wheel bearing is frictionless and the string does not slip. find the tension and the acceleration of the object.

    I think mg-T=ma


    and that I=MR^2

    thats all i know can someone help me please

    thank you
     
  2. jcsd
  3. Jan 4, 2004 #2

    Doc Al

    User Avatar

    Staff: Mentor

    You need to apply Newton's 2nd law to each body: the mass and the wheel.
    Right. That's Newton's 2nd law applied to the mass.

    Now apply it to the wheel, using the rotational form: Torque = I*α (you tell me the torque).

    To relate the two equations, note that a = R*α.
     
  4. Jan 4, 2004 #3
    Hi Doc Al,

    Almost solved it
    the a i use here will be angular acceleration

    so

    net torque=T*R or

    Ia=T*R

    Ia=(mg-mRa)R

    Ia=mgr-mR^2a

    Ia+mgR^2a=mgr
    a(Ia+mR^2)=mgr

    a=mgr/I+mR^2

    for acceleration the tension is a=mR^2g/(I+mr^2)
     
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