Two metallic spheres S1 and S2 are made of the same material and have identical surface finish. The mass of S1 is three times that of S2. Both the spheres are heated to the same high temperature and placed in the same room having lower temperature but are thermally insulated from each other. The ratio of the initial rate of cooling of S1 to that of S2 is

Rate of cooling (R) = ∆θt = A∈0σ(T4-T04)mc⇒  R is directly proportional to Am directly proportional to Area Volumedirectly proportional to r2r3= 1r⇒  Rate (R) directly proportional to 1r directly proporitonal to 1m13                                                                 [m = ρ ×43πr3   ⇒  r directly proportional to m13]⇒ R1R2 = (m2m1)13  = (13)13