# physics

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

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

1. (a) Erotation = (1/2)I*w^2

where I = (2/5)M R^2 and
w is the angular rotation rate of the earth in radians per second (which you should calculate).
You will need to calculate w and look up the mass and radius of the earth. You wil be making as assumption that the earth is uniformly dense, although it really isn't.

(b) Ekinetic = (1/2) M V^2

where V is the orbital speed.

posted by drwls

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