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

Answer

hollow sphere

Explanation

The hollow sphere cools faster. We know that the rate of cooling is inversely proportional to the internal capacity of the body. The thermal capacity i.e., the product of mass and specific heat is smaller for a hollow sphere than for a solid sphere as the hollow sphere has lesser mas than the solid sphere, the hollow sphere will cool faster.