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**[SOLVED] Homework help very urgent!!!! plz help**

The potential energy of an object due to its own gravity is of order

Potential Energy ~

GM2

r

where M is the body's mass and r is its radius. There is a factor in this equation that depends on the density distribution within the

object (e.g. 0.6 for a uniform sphere) - but for rough calculations we can ignore that.

Using preceeding approximation.

So I need to calculate the potential energy stored in the self-gravity of the sun, assuming a solar radius of

6.96μ108m and solar mass of 2.0μ1030kg.

I also need to calculate the total power radiated by the sun assuming the temperature of the stellar

photosphere is a 6000° K blackbody and estimate the lifetime of the sun if its energy source was purely locked-up gravitational

energy.

I'm stuck on all three of them since my physcis and math aren't strong, so can anyone please help me onto how to start off! Thanx!!!^^