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U. Phys

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What is the angular momentum of a 3.7kg uniform cylindrical grinding wheel of radius 25cm when rotating at 1500rpm?


How much torque(in magnitude) is required to stop it in 5.0s?

Could you explain this in detail, I don't really understand torque and momentum well.

  • U. Phys - ,

    You need to separate linear motion from rotational.

    Read in two columns
    mass kg...........momentofinertia kg*m^2
    displacement m...angular displacement rad
    velocity m/s ....ang velocity rad/s^2
    acceleration m/s^2.ang acc rad/s^2

    and finally, memorize this
    tangential velocity on a curve= radius*ang velocity

    Now your question.
    ang momentum=I*w
    (that is ang momentum is momentofinertia * angular velocity)
    So you need I for a solid disk, make you a convenient card with common shapes..http://en.wikipedia.org/wiki/List_of_moments_of_inertia
    Using thin disk model, I= mr^2/2
    ang momentum= mr^2/2 * 1500rev/min*1min/60sec*2PIrad/rev

    b) Torque= I*angacceleration= I*(wf-wi)/time= mr^2/2(-1500*2PI/60)

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