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Homework Help: Torque, energy, and average power

  1. Jan 3, 2006 #1
    Calculate the torque (in N*m), energy (in J), and average power (in W) required to accelerate the Earth in 3 days from rest to its present angular speed about its axis.
  2. jcsd
  3. Jan 3, 2006 #2


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    Gold Member

    You need to show your work or we can't help you.
  4. Jan 3, 2006 #3
    t = I*a

    rotational inertia of a solid sphere = 2/5*m*r^2
    mass of earth = 5.9742*10^24 kg
    radius of earth = 6378.1 km
    rotational inertia of the earth = 9.72126*10^31

    a = delta v / delta t
    angular speed of the earth = 7.27*10^-5 rad/s
    3 days = 259200 seconds
    a = (7.27*10^-5)/(259200) = 2.80478*10^-10

    torque = (9.72126*10^31)*(2.80478*10^-10) = 2.7266*10^22 N*m

    But this answer is wrong, I don't know why... please help me. Am I on the right track, am I using the correct equations?
  5. Jan 3, 2006 #4
    Check this one. Should be ~ 9.7*10^37 kgm^2

    Also you have not written the units for some quantities. Units matters.

  6. Mar 28, 2008 #5
    You probably didn't change the radius of the earth to meters. :)
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