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April 26, 2015

Homework Help: Physics

Posted by Jim on Wednesday, March 28, 2007 at 12:40pm.

Calculate the kinetic energy that the earth has because of its rotation about its own axis. Assume that the earth is a uniform sphere and that its path around the sun is circular. For comparison, the total energy used in the United States in one year is about 9.33 109 J.


Calculate the kinetic energy that the earth has because of its motion around the sun.


In either case, the trick is to calculate the moment of inertial.
In the first case, the moment of inertia of a solid sphere rotating about its axis.

In the second case, MassEarth*distancefromSun^2.

Then, KE= 1/2 I* radiusofrotation^2

Please check. The answer i came up with is wrong.

a.
rotational KE = 1/2(Iw^2)
=1/2(2/5mr^2)w^2
=1/2((2/5(5.98x10^24kg)(6.38x10^6m))(2PI rad/ s)^2
=(7.63048x10^30kg*m)(39.4384/2.49x10^-13)
= 1.210 x 10^18

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