Question

a metallic tyre is heated first before fixing it into the rim of a wheel of cart. explain why

Answer 1

Metals expand on heating and contract on cooling. This expansion and contraction of a metal is a reversible change. The metallic rim used is slightly smaller in diameter than the wheels .On heating the rim expands. And can easily lie on the wheels. When the rim cools, it contract and press tightly on to the wheels. 

Answer 2

the metallic tyre is heated to fix into a rim of the wheel as it can fix easily without any problem as the shape of the rim decreases and then it can be fixed easily.