Newton’s Third Law of Motion MCQs Quiz | Class 9

This quiz covers Class IX Science (Code 086), Unit III: Motion, Force and Work, specifically focusing on Newton’s Third Law of Motion. The questions test your understanding of the statement of the law and various action-reaction pairs encountered in daily life. Please answer the 10 MCQs below, then click Submit to view your score and download the PDF answer sheet.

Understanding Newton’s Third Law of Motion

Newton’s Third Law of Motion describes the nature of forces between two interacting objects. It states that for every action, there is an equal and opposite reaction. This implies that forces always exist in pairs and cannot exist in isolation.

Key Characteristics

  • Interaction: Forces are interactions between two different bodies.
  • Different Objects: Action and reaction forces act on two different objects, never on the same object. This is why they do not cancel each other out to produce zero net force on a single body.
  • Simultaneous: The action and reaction forces occur at the exact same instant.
  • Direction: The forces are directed exactly opposite to each other.

Common Examples

Scenario Action Force Reaction Force
Walking Foot pushes ground backward Ground pushes foot forward
Swimming Swimmer pushes water backward Water pushes swimmer forward
Firing a Gun Gun exerts force on bullet Bullet exerts recoil force on gun
Rocket Launch Rocket pushes exhaust gases down Gases push rocket up

Quick Revision Points

  • Action and reaction are equal in magnitude but opposite in direction.
  • Even though forces are equal, the accelerations produced may differ if the masses of the two bodies are different (F = ma).
  • The law applies to all types of forces, including contact forces and gravitational forces.

Extra Practice Questions

  1. Why does a hose pipe push backward when water rushes out of it?
  2. If a fly hits a moving bus windshield, does the fly or the bus experience a greater force? (Answer: Both experience the same force magnitude).
  3. Explain how a bird flies using the third law of motion.
  4. Why is it difficult to walk on a slippery surface (frictionless) regarding the third law?
  5. Identify the action and reaction pairs when a book rests on a table.