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Homework Help: Torque energy

  1. Dec 8, 2005 #1
    A disc of moment of inertia 23.4 kg m2 is made to rotate about an axis through its centre by a torque of T . The disc starts from rest, and after {t} s has kinetic energy 632.2 J. Calculate the angular velocity (in rad s-1) after {b} s.

    if i work out the angular velocity from the KE=0.5*I*w^2 this equation how do i use it work out the angular momentum from t to b.
  2. jcsd
  3. Dec 8, 2005 #2


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    The problem doesn't actually ask for angular momentum, but you should be able to figure out the angular momentum from the moment of interia, and the angular velocity.
  4. Dec 9, 2005 #3
    I have a doubt. Does something called as torque energy really exist. I have understood that torque is something imagined and does not actually exist fromthe explanation given to me on the post "right hand rule" in Gen Phys. Someone please explain.
  5. Dec 9, 2005 #4

    Doc Al

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    What you are calling "torque energy" is just rotational kinetic energy. Why in the world would you think that torque is just something "imagined"?
  6. Dec 10, 2005 #5
    I interpreted that right hand rule can be replaced by lefthand rule, so the direction of things like torque isn't fixed. It is just a convention. Anyway the explanation wasn't clear to me. The above reasons led me to the conclusion that the torque is just something imagined and does not really exist. I understood that I am through a wrong way. Please direct me in proper way.
  7. Dec 10, 2005 #6
    Direction of a torque may be defined in a conventional way but that doesn't mean it doesn't exist. Torques are just turning forces (or coupled linear forces). Have you never seen anything turn or rotate? (rhetorical question). Of course torques exist.

    ang momentum = moment of inertia * ang velocity
    (you have everything you need for the calculation)
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