Q. Two spheres of radii R1 and R2 have densities d1 and d2 and specifc heats C1 and C2. If they are heated to the same temp., the ratio of their rates of cooling will be ---------------.

By Stefan 's law  -(dQ/dt)=Ae*(stefan const)*T^4

dQ=ms(dT)

from 2 eqns get

-(dT/dt)=(Ae*(stefan const)*T^4)/(ms)

m=(4/3*pi*r^3)*(density)

substitute the values in the eqn and get (R2*d2*c2)/(R1*d1*c1)