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Find moment of inertia via torque and acceleration parameter

  1. Feb 4, 2015 #1
    1. The problem statement, all variables and given/known data
    2-1. A constant torque of 4 Nm is applied to an unloaded motor at rest at time t = 0. The motor reaches a speed of 1717 rpm in 4 s. Assuming the damping to be negligible, calculate the motor inertia in Nm·s2.

    2. Relevant equations
    T = J(eff) * dw/dt
    J = kg*M^2

    3. The attempt at a solution
    I have NO clue where to start. First question - why is the motor inertia units stated as Nm*S2? I thought moment of inertia was only kg*m^2 (m = meters).
    Second question - can someone point me in the right direction? I have been reading for hours. I know this is simple I'm just missing a link. Thanks for the help.
    Also the problem seems basic but I posted it in this section because its for a 4000 level course - Electric Drives. Let me know if it should be elsewhere.
     
  2. jcsd
  3. Feb 4, 2015 #2

    rock.freak667

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    Homework Helper

    1 N = 1 kg * 1 ms-2

    In your first relevant equation, how would you calculate dw/dt?
     
  4. Feb 4, 2015 #3
    Wow. I feel like an idiot. Got it. Thanks.
     
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