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

Since the temperature and surface area is same,
therefore the energy emitted per second by both spheres is
same.
We know that `Q=mcDeltaT`
Since Q is same and c is also same (both copper).
`:. Mprop1/(DeltaT)`
Mass of hollow sphere is less,
`:.` Temperature change will be more.
`:.` Hollow sphere will cool faster.