Test your knowledge with this TNPSC Physics Laws of Motion Quiz featuring important MCQs. Evaluate your understanding of Newton’s Laws, force, momentum, and related concepts while preparing for competitive exams. Build a strong foundation in Laws of Motion by attempting this TNPSC Physics Laws of Motion Quiz.
TNPSC Physics Laws of Motion Quiz 2 – Detailed Explanations
Newton’s laws of motion form the foundation of classical mechanics and are one of the most important topics in TNPSC physics MCQs. These laws explain how objects behave when forces act on them, helping us understand real-life situations like moving vehicles, walking, jumping, and even rocket motion. Most TNPSC laws of motion questions are directly based on concepts like inertia, force, acceleration, and action-reaction pairs.
1. Which law explains why passengers fall backward when a bus starts suddenly?
Newton’s First Law of Motion states that an object remains at rest or continues to move with uniform velocity unless acted upon by an external force. This property of resisting any change in the state of rest or motion is called inertia. When a bus starts suddenly, the lower part of a passenger’s body moves forward along with the bus because it is in contact with the floor, while the upper body tends to remain at rest due to inertia. As a result, the passenger appears to fall backward. This is one of the most common real-life examples of the inertia of rest.
Key Points:
- Newton’s First Law is also known as the Law of Inertia.
- Inertia is the tendency of a body to resist changes in its state of motion.
- Greater mass means greater inertia.
- Everyday examples of inertia are frequently asked in TNPSC examinations.
Exam Tip: Passengers falling backward when a bus starts suddenly and dust coming off a carpet when it is shaken are classic examples of inertia of rest.
✅ Correct Answer: A. Newton’s First Law
2. The acceleration of a body increases when:
According to Newton’s Second Law of Motion, the acceleration of an object depends directly on the net force acting on it and inversely on its mass. This relationship is expressed by the equation F = ma. If the mass of an object remains constant, increasing the applied force produces greater acceleration. Therefore, a stronger push or pull causes an object to speed up more quickly.
Key Points:
- Newton’s Second Law relates force, mass, and acceleration.
- Acceleration increases when force increases.
- For the same force, a heavier object accelerates less than a lighter one.
- SI unit of force is the newton (N).
Exam Tip: Remember the formula F = ma. In TNPSC questions, if mass is constant, more force means more acceleration.
✅ Correct Answer: C. Force increases
3. Which quantity is directly proportional to force?
Newton’s Second Law states that the net force acting on an object is directly proportional to its acceleration when the mass remains constant. This means that if the applied force doubles, the acceleration also doubles. The relationship between force and acceleration is one of the fundamental principles of mechanics and is widely used to explain the motion of objects.
Key Points:
- Force and acceleration are directly proportional.
- Mass must remain constant for this relationship.
- Formula: F = ma
- Acceleration is measured in m/s².
Exam Tip: Whenever you see the phrase “directly proportional to force,” think of acceleration.
✅ Correct Answer: B. Acceleration
4. When a rug is shaken, dust falls off due to:
Dust particles resting on a rug possess inertia of rest, meaning they tend to remain in their original position. When the rug is shaken suddenly, the rug moves but the dust particles resist this change because of inertia. As a result, the dust separates from the rug and falls to the ground. This demonstrates Newton’s First Law of Motion.
Key Points:
- Dust initially remains at rest due to inertia.
- The rug moves suddenly, but the dust does not move immediately.
- This difference in motion causes the dust to fall off.
- It is an example of inertia of rest.
Exam Tip: Dust falling from carpets, rugs, or clothes when shaken is a standard example of inertia in competitive exams.
✅ Correct Answer: C. Inertia
5. A heavier body has more:
Inertia is the property of matter that resists changes in its state of rest or motion. The amount of inertia depends only on the mass of the object. Since a heavier body has greater mass, it possesses greater inertia and requires more force to change its state of motion than a lighter body.
Key Points:
- Inertia depends only on mass.
- Greater mass means greater inertia.
- Heavier objects are more difficult to start, stop, or change direction.
- Inertia is not the same as force or momentum.
✅ Correct Answer: B. Inertia
6. Which law explains the motion of rockets?
The motion of a rocket is explained by Newton’s Third Law of Motion, which states that for every action, there is an equal and opposite reaction. When a rocket burns fuel, it expels hot gases downward at high speed (action). In response, an equal and opposite force pushes the rocket upward (reaction). This action-reaction pair allows the rocket to move even in the vacuum of space, where there is no air to push against.
Key Points:
- Newton’s Third Law states that every action has an equal and opposite reaction.
- Rockets move by expelling gases downward.
- The reaction force pushes the rocket upward.
- Air is not required for rocket propulsion.
Exam Tip: Questions on rockets, gun recoil, walking, swimming, rowing a boat, and jumping from a boat are common applications of Newton’s Third Law.
✅ Correct Answer: C. Third Law
7. If no external force acts on an object, it will:
According to Newton’s First Law of Motion, an object remains at rest or continues to move with a constant velocity in a straight line unless acted upon by an external force. This means that if no external force such as friction, gravity, or a push acts on the object, its speed and direction remain unchanged. The law demonstrates the natural tendency of objects to maintain their existing state of motion.
Key Points:
- An external force is required to change an object’s motion.
- Without external force, velocity remains constant.
- Constant velocity means both speed and direction remain unchanged.
- Newton’s First Law is also called the Law of Inertia.
Exam Tip: If a question mentions “no external force”, the answer is usually constant velocity or state of rest.
✅ Correct Answer: A. Move with constant velocity
8. Which of the following is a vector quantity?
A vector quantity has both magnitude and direction, whereas a scalar quantity has only magnitude. Acceleration describes how quickly the velocity of an object changes and also indicates the direction of that change. Therefore, acceleration is a vector quantity. In contrast, speed, distance, and time do not have direction and are scalar quantities.
Key Points:
- Vectors have magnitude and direction.
- Acceleration is measured in m/s².
- Speed, distance, and time are scalar quantities.
- Force, velocity, momentum, and acceleration are important vectors.
Exam Tip: Remember the common vector quantities: Force, Velocity, Acceleration, Momentum, and Displacement.
✅ Correct Answer: D. Acceleration
9. The SI unit of mass is:
Mass is the amount of matter present in an object. The SI unit of mass is the kilogram (kg), which is the standard unit used worldwide in science and engineering. Mass does not change with location, unlike weight, which depends on gravity. It is one of the seven fundamental SI base quantities.
Key Points:
- SI unit of mass is kilogram (kg).
- Mass measures the quantity of matter.
- Mass remains constant regardless of location.
- Weight is measured in newtons (N).
Exam Tip: Do not confuse mass (kg) with weight (N) in competitive examinations.
✅ Correct Answer: B. Kilogram
10. When mass decreases, acceleration:
Newton’s Second Law states that Force = Mass × Acceleration (F = ma). Rearranging the equation gives Acceleration = Force ÷ Mass. If the applied force remains constant, reducing the mass increases the acceleration. This is why lighter objects can accelerate more quickly than heavier objects under the same force.
Key Points:
- Acceleration is inversely proportional to mass.
- Lower mass results in higher acceleration for the same force.
- Formula: a = F/m
- Both mass and force influence acceleration.
Exam Tip: For a constant force:
- Increase mass → Decrease acceleration.
- Decrease mass → Increase acceleration.
✅ Correct Answer: D. Increases
11. Which law is applied when we walk on the ground?
Walking is a practical application of Newton’s Third Law of Motion. When we walk, our feet push the ground backward. In response, the ground exerts an equal and opposite force on our feet, pushing us forward. This action-reaction pair enables us to move. Without sufficient friction between our feet and the ground, walking would not be possible.
Key Points:
- Walking depends on Newton’s Third Law.
- The foot pushes the ground backward.
- The ground pushes the body forward.
- Friction provides the necessary grip for walking.
✅ Correct Answer: C. Third Law
12. The resistance of a body to change its motion is called:
Inertia is the property of matter that resists any change in the state of rest or motion of an object. According to Newton’s First Law, every object tends to maintain its existing state unless acted upon by an external force. The greater the mass of an object, the greater its inertia. Inertia itself is not a force but a natural property of all matter.
Key Points:
- Inertia resists changes in motion.
- It depends only on the mass of the object.
- Greater mass means greater inertia.
- Newton’s First Law explains inertia.
Exam Tip: Remember the three types of inertia:
- Inertia of Rest
- Inertia of Motion
- Inertia of Direction
✅ Correct Answer: A. Inertia
13. A ball thrown upward slows down due to:
When a ball is thrown upward, the gravitational force of the Earth acts continuously in the downward direction. This force opposes the upward motion of the ball, causing its velocity to decrease gradually until it becomes zero at the highest point. After reaching the maximum height, gravity causes the ball to accelerate downward toward the Earth.
Key Points:
- Gravity always acts toward the Earth’s center.
- Upward velocity decreases because of gravity.
- At the highest point, the velocity becomes zero momentarily.
- The acceleration due to gravity is approximately 9.8 m/s² downward.
✅ Correct Answer: B. Gravity
14. Which of the following is NOT a vector quantity?
Speed is a scalar quantity because it has only magnitude and no direction. Vector quantities require both magnitude and direction. Force, velocity, and acceleration are vectors because they describe not only how much but also in which direction an object acts or moves.
Key Points:
- Speed is a scalar quantity.
- Velocity is a vector quantity.
- Force and acceleration are also vectors.
- Scalars have magnitude only.
Exam Tip: A quick memory trick:
- Speed = Scalar
- Velocity = Vector
✅ Correct Answer: C. Speed
15. The rate of change of momentum is equal to:
Newton’s Second Law of Motion states that the net force acting on an object is equal to the rate of change of its momentum. Momentum is the product of mass and velocity (p = mv). Whenever the momentum of an object changes due to a force, the magnitude of that force equals the rate at which the momentum changes.
Key Points:
- Momentum = Mass × Velocity.
- Force changes the momentum of an object.
- Newton’s Second Law can be expressed using momentum.
- SI unit of force is newton (N).
- F = ma
- Force = Rate of change of momentum
✅ Correct Answer: D. Force
16. When a person jumps off a boat, the boat moves backward due to:
When a person jumps forward from a boat, they push the boat backward with their feet. According to Newton’s Third Law of Motion, the boat exerts an equal and opposite force on the person, pushing them forward, while the boat moves backward. This action-reaction pair causes both the person and the boat to move in opposite directions.
Key Points:
- Newton’s Third Law explains the motion.
- Action and reaction forces act on different bodies.
- The boat moves backward as the person moves forward.
- Similar examples include rocket launches and gun recoil.
Exam Tip:
Questions involving boats, rockets, guns, swimming, and walking are commonly based on Newton’s Third Law.
✅ Correct Answer: C. Third Law
17. Acceleration is zero when:
Acceleration is defined as the rate of change of velocity. If an object’s velocity remains constant, there is no change in either its speed or direction, so its acceleration is zero. An object moving with constant velocity is said to be in uniform motion, provided no unbalanced external force acts on it. This is consistent with Newton’s First Law of Motion.
Key Points:
- Acceleration occurs only when velocity changes.
- Constant velocity means constant speed and constant direction.
- Zero acceleration indicates uniform motion.
- SI unit of acceleration is m/s².
Exam Tip:
Remember: Constant velocity = Zero acceleration, but constant speed alone does not always mean zero acceleration if the direction changes (e.g., circular motion).
✅ Correct Answer: B. Velocity is constant
18. Which quantity depends on both mass and velocity?
Momentum is the quantity of motion possessed by an object and is calculated using the formula p = mv, where m is mass and v is velocity. This means that momentum increases if either the mass or the velocity increases. Heavy and fast-moving objects have greater momentum than light or slow-moving objects.
Key Points:
- Momentum depends on both mass and velocity.
- Formula: p = mv.
- SI unit of momentum is kg·m/s.
- Greater mass or greater velocity results in greater momentum.
✅ Correct Answer: C. Momentum
19. Which law explains why we cannot move a wall by pushing it?
According to Newton’s Third Law of Motion, every action has an equal and opposite reaction. When a person pushes a wall, the wall exerts an equal force in the opposite direction. Since the wall is firmly supported and has a very large mass, it does not move noticeably. The equal and opposite reaction force prevents the wall from being pushed forward.
Key Points:
- Newton’s Third Law involves action and reaction forces.
- Action and reaction act on different bodies.
- The wall exerts an equal and opposite force on the person.
- A very large mass makes the wall’s acceleration negligible.
✅ Correct Answer: A. Third Law
20. A rolling ball eventually stops due to:
A rolling ball gradually comes to rest because friction acts between the ball and the ground. Friction is a force that always opposes the direction of motion. As the ball rolls, friction continuously reduces its speed by converting some of its kinetic energy into heat. Eventually, the ball loses all its motion and stops.
Key Points:
- Friction opposes motion.
- It reduces the speed of moving objects.
- Kinetic energy is converted into heat due to friction.
- Without friction, the ball would continue moving for a much longer time.
✅ Correct Answer: B. Friction
Important Points to Remember
- Inertia depends on mass (more mass → more inertia)
- Force = mass × acceleration (F = ma)
- Acceleration is directly proportional to force
- Acceleration is inversely proportional to mass
- Momentum = mass × velocity
- Rate of change of momentum = force
- Action and reaction always act on different bodies
- Friction always opposes motion
- Gravity slows down upward motion and speeds up downward motion
- If no external force acts → object continues in same state (rest/motion)
Real-Life Examples of Newton’s Laws
For First Law (Inertia)
- Passengers fall backward when a bus starts suddenly
- Dust comes off when a carpet is shaken
- Seat belts prevent forward motion during sudden stops
Second Law (F = ma)
- An empty cart moves faster than a loaded cart
- Kicking a football is easier than kicking a stone
- Heavier objects require more force to move
Third Law (Action–Reaction)
- Rockets move upward by pushing gases downward
- While walking, we push the ground backward
- Swimming: pushing water backward moves us forward
Most TNPSC questions are based on identifying these real-life applications of Newton’s laws.
Further Reading:
Deepen your understanding of Laws of Motion by reading the official NCERT chapter link given below. It explains force, inertia, Newton’s Laws, and momentum with simple examples, making it an excellent resource for TNPSC General Science preparation.
Authority: NCERT Class 9 Science – Chapter 9: Force and Laws of Motion
