Mass density(mass per unit volume) of a sphere is varying as ρ = (1 + 2r) kg/m^3 where r is the distance of the position of the point from the centre of sphere(in metre). Calculate mass of the sphere if R is the radius of the sphere?
Ans: 4π[(R^3/3) + (R^4/2)]
How do we find the answer?
let us take a small sphere at a distance x from centre of thickness dx
mass of this small sphere is dm.volume of this sphere
=4pix^2dx(neglecting higher power of dx)
[int x^n=[x^(n+1)]/n+1 where int means integration]
now integrate taking limit of RHS 0 to R.
Finally you will get