Taking small element for integration purpose in SOLID sphere?

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



The Question originally is to find the m of a solid uniformly charged solid sphere which is rotating uniformly with ω



Now

2. Relevant equations



Now my question to you is how to take the small element?









3. The attempt at a solution



i take a small disc with radius rsinθ.



Now a= ∏(rsinθ)^2



i= q/t= dq/(2∏/w)



where dq= rho times dv= 2∏rsinθ times rdθ.



now this gives the relevant answer but why is it that i cant take a small element of a small sphere?



because i cant decribe m for that too?



It's just that i dont recall taking a disc as a small element in case of solid sphere :~(

via Physics Forums RSS Feed http://www.physicsforums.com/showthread.php?t=725422&goto=newpost