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Homework Help: Conceptual Question on Net Torque

  1. Mar 25, 2008 #1
    A constant nonzero net torque is exerted on an object. Which of the following can not be constant? Choose all that apply.

    -angular position
    -angular velocity
    -angular acceleration
    -location of center of mass
    -moment of inertia
    -kinetic energy

    My guess is that angular position and angular velocity can not be constant, but I'm not 100% sure. Can anyone help me here?
  2. jcsd
  3. Mar 25, 2008 #2


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    You are correct that the angular velocity and angular position cannot be constant but if those are changing, will some of the other quantities also change?


    If the angular velocity changes, what other option(s) will change?
    Last edited: Mar 25, 2008
  4. Mar 25, 2008 #3
    I see, so according to the kinematics of angular properties, if angular position and angular speed is not constant, than that means that the angular acceleration is not constant either. The moment of inertia depends on Mass and distance from the axis, so since those are constants, the moment of inertia are constant right? And since kinetic energy (rotational) depends on moment of inertia (constant) and angular speed(non-constant), then kinetic energy is also not constant.

    So this is my answer for the problem:

    Angular Position
    Angular Speed
    Angular Acceleration
    Kinetic Energy

    Are all non-constants


  5. Mar 25, 2008 #4
    Why is angular acceleration not constant?
    Do you know an equation relating angular acceleration, net torque and the moment of inertial.
  6. Mar 25, 2008 #5
    Okay, so I think I should use this equation torque = I*alpha
    Where alpha(angular acceleration) has to be constant because I is constant and the net torque is constant.

    So therefore, my answer should be:

    Angular Position
    Angular Speed
    Kinetic Energy

    Are all non-constant.

    Is this correct? Can anyone check this for me please?

  7. Mar 25, 2008 #6
    Can anyone confirm my answer above?
  8. Mar 25, 2008 #7


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    I agree with your latest answer.
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