$(a)$ Define inertia. You are provided with three bodies made of wood,rubber,and iron of the same shape and size. Which one of them will have greater inertia? Explain it.
$(b)$ When a striker hits the bottom of the pile of coins placed at the centre of a carom board,only the lowest coin is removed. Give reason for it.

(D) Inertia is the property of a body by virtue of which it resists any change in its state of rest or of uniform motion in a straight line. Among wood,rubber,and iron of the same shape and size,the iron body will have the greatest inertia. This is because mass is the measure of inertia; since iron has the highest density and thus the greatest mass among the three,it possesses the greatest inertia.
$(b)$ This phenomenon is due to the inertia of rest. When the striker hits the lowest coin,it suddenly comes into motion due to the applied force. However,the rest of the coins in the pile remain in their state of rest due to their inertia of rest. Consequently,they fall vertically downwards into the same position as the bottom coin moves away.