1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: 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


    User Avatar
    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.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted