A solid sphere of copper of radius R and a hollow sphere of the same materail of inner radius r and outer radius A are heated to the same temperature and allowed to cool in the same environment. Which of tehm starts cooling faster?

Explanation

As outer radius is same at same temperature, radiation power will be same so we use
`(dQ)/(dt)=ms(dT)/(dt)`
`implies` Rate of cooling `(dT)/(dt)=(1)/(ms)(dQ)/(dt)`
Thus lower mass hollowsphere will cool faster