A solid copper cube and a solid copper sphere, both of same mass & emissivity are heated to same initial temperature and kept under identical conditions.  What is the ratio of their initial rate of fall of temperature?

If 'a' is the length of cube, surface area Scube=6a2 If 'r' is the radius of sphere, surface area  Ssphere=4πr2Both the cube and sphere have the same volume as given Volume  V=a3  ∵V=43πr3∴a3=43πr3⇒ar=4π313 Area cube  Area sphere =6a24πr2=64πar2=64π×4π323=6π13∵  mass are equal Rate of fall in temperature = Surface area∵Rate of fall in temperature= 6π13