A man pulls one end of a rigid rod attached to a block of mass 10 kg on a smooth horizontal surface with a force of F₁ = 24N horizontally. The rod has a mass of 2 kg. Find the contact force between rod and the block.

Since total mass of the system is 12 kg, so acceleration of system as whole 24/12 = 2 m/s².

Since the system is rigid the rod as well as block will have this acceleration.

Now, if we take free body diagram of rod and block.

Where F₁ in the internal force on the contact force between rod and block, and we order block

F₁ = 10 × 2 = 20 N

So, contact force is 20 N.