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**1. The problem statement, all variables and given/known data**

What is the Kinetic energy of a 180-kg satellite which circles the earth (radius=6.4x10^6m, mass=6.0x10^24kg) with a period of 8.0 h?

a)2.2x10^9J

b)2.0x10^9J

c)1.8x10^9J

d)2.4x10^9J

e)3.6x10^9J

**2. Relevant equations**

Ep= GM1M2/r

Ek=.5Mv^2

Ac=(4[tex]\pi[/tex]^2r)/T^2

v=-[tex]\omega[/tex]^2r

Ep=Ek

**3. The attempt at a solution**

The radius that the satellite is orbiting is not given only earths radius, i tried to use ratios but this cannot work as the satellite is moving much faster than earth. Then i tried a guess and check method with the given options trying to cross check the speed. Eventually i got an answer of 1.8x10^9J which is correct. There must be a better method for calculating the radius of the satellite?????