# Physics- drwls please help

posted by
**Jim**
.

(a) 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.

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

Please check. The answer i came up with for a. 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

ur answer is right. I do belive

I don't understand where you got the w^2 The earth's rotational w is

(2 pi rad)/(24*3600 sec) = 7.27*10^-5 rad/s