Question

Consider an expanding sphere of instantaneous radius R whose total mass remains constant. The expansion is such that the instantaneous density ρ remains uniform throughout the volume. The rate of fractional change in density (1/ρ dρ/dt)  is constant. The velocity v of any point on the surface of the expanding sphere is proportional to
(A) R 

(B) R³

(C)1/R

(D) R^2/3

Answer 1

The velocity v of any point on the surface of the expanding sphere is proportional to R