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Find mom of inertia and frictional torque

  1. Jan 6, 2013 #1
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
    Last edited: Jan 6, 2013
  2. jcsd
  3. Jan 6, 2013 #2

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    Welcome to PF, physicsgirl4! :smile:

    That's the right value!

    But the wrong unit...
    You converted revolutions to radians, and it's an angular acceleration instead of a angular velocity.
    The unit should be rad/s2.

    You seem to have lost a pi here...
    But the value is not correct yet anyway, since you haven't taken friction into account yet.

    Let's set up the equations first:

    In the first stage:
    $$T_{net} = T_{ext} - T_{fric} = I \cdot \alpha_1$$
    $$T_{ext} = 60 N m$$
    $$\alpha_1 = {800 \cdot 2\pi \over 60 \cdot 12} {rad \over s^2}$$

    In the second stage:
    $$- T_{fric} = I \cdot \alpha_2$$
    $$\alpha_2 = - {800 \cdot 2\pi \over 60 \cdot 100} {rad \over s^2}$$

    This is a set of equations, can you solve it?
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