How Long Could Gravitational Contraction Power the Sun?

[Tuugii]

Homework Statement

The gravitational potential energy W of a self-gravitating sphere of mass M and radius R depends on the detailed distribution of mass within the sphere, but it is generally of order of magnitude -GM^2/R. For the Sun, W_sun = -2G(M_sun)^2/R. What is the timescale
t = -(1/2)(W_sun)/(L_sun) over which gravitational contraction could have supplied the power radiated by the sun at it's present rate?

please give some hints, thanks a lot.

 

[malawi_glenn]

what is L_sun ?

(iknow that it is Luminosity, but try to find the value)

 

[Tuugii]

what is L_sun ?

(iknow that it is Luminosity, but try to find the value)

thanks for the reply. But I didn't understand what was your hint... :)

 

[malawi_glenn]

thanks for the reply. But I didn't understand what was your hint... :)

I meant, have you tried just to plug in the value of L_sun into that eq?