Which of the following laws explains why it is difficult to fix a nail on a freely suspended wooden frame?

Correct answer: (c) Newton's third law of motion

Explanation

By Newton's third law, every action has an equal and opposite reaction. When a hammer strikes a nail, the nail pushes into the wood only if the wood pushes back on it with an equally large force.

A frame fixed to a wall can supply this reaction. A freely suspended frame cannot: it simply gives way and swings back with the blow, so the nail does not go in. A firm support behind the frame (or a heavy frame) is needed to fix the nail.