Test your preparation with Laws of Motion Quiz 4, designed for TNPSC aspirants. This quiz covers important questions on Newton’s Laws of Motion, force, inertia, momentum, and everyday applications. Practice these exam-oriented MCQs with answers and explanations to strengthen your TNPSC Physics preparation.
TNPSC Physics – Laws of Motion Quiz 4 – Detailed Explanations
Master the fundamental concepts with our detailed explanations for Laws of Motion TNPSC Questions. Each explanation is designed to help you understand Newton’s Laws of Motion, force, inertia, momentum, and their real-life applications instead of simply memorizing the answers. Whether you’re preparing for the TNPSC exam or other competitive examinations, these concept-based explanations will strengthen your understanding, improve problem-solving skills, and help you answer similar questions with confidence.
1. Why does a passenger lean forward when a moving bus suddenly stops?
This question is based on Newton’s First Law of Motion, also known as the Law of Inertia. When a moving bus stops suddenly, the bus comes to rest immediately, but the passenger’s body tends to continue moving forward due to inertia. Unless an external force, such as a seat belt or the seat itself, acts on the passenger, the body resists the change in its state of motion.
Key Points:
- Newton’s First Law is also called the Law of Inertia.
- Inertia is the tendency of an object to resist changes in its state of motion.
- Greater mass means greater inertia.
Real-Life Example:
Passengers are advised to wear seat belts because they prevent the body from moving forward during sudden braking.
✅ Correct Answer: A. First Law
2. A force acting on a body for a short time is known as:
Impulse is the effect produced when a force acts on an object for a short period. It is equal to the product of force and the time for which it acts. Even a large force acting for a very short duration can significantly change an object’s momentum.
Key Points:
- Impulse = Force × Time.
- Impulse changes the momentum of an object.
- It is measured in newton-second (N·s).
Real-Life Example:
An airbag increases the time of impact during a collision, reducing the force on passengers.
✅ Correct Answer: B. Impulse
3. Which of the following increases when the velocity of an object increases?
Momentum depends on both the mass and velocity of an object. If the mass remains constant, increasing the velocity increases the momentum proportionally. Faster-moving objects are therefore more difficult to stop because they possess greater momentum.
Key Points:
- Momentum = Mass × Velocity.
- Momentum increases with velocity when mass is constant.
- Momentum is a vector quantity.
Real-Life Example:
A fast-moving motorcycle has greater momentum than the same motorcycle moving slowly.
✅ Correct Answer: C. Momentum
4. Why do we push harder to move a heavy object than a light one?
Heavy objects have more mass, and greater mass means greater inertia. Because inertia resists any change in motion, a larger force is required to start moving a heavier object than a lighter one.
Key Points:
- Inertia depends only on mass.
- Heavy objects have greater inertia.
- More force is needed to overcome greater inertia.
Real-Life Example:
Pushing a loaded trolley requires more effort than pushing an empty trolley.
✅ Correct Answer: B. More inertia
5. A cricket ball and a tennis ball are hit with the same force. Which one experiences greater acceleration?
According to Newton’s Second Law of Motion, acceleration is directly proportional to force and inversely proportional to mass. Since the tennis ball has less mass than the cricket ball, it experiences greater acceleration when the same force is applied.
Key Points:
- Newton’s Second Law: Force = Mass × Acceleration (F = ma).
- For the same force, a lighter object accelerates more.
- Acceleration decreases as mass increases.
Real-Life Example:
An empty shopping cart accelerates more easily than a fully loaded cart when pushed with the same force.
✅ Correct Answer: A. Tennis ball
6. Why do cyclists bend forward while riding fast?
Cyclists bend forward to reduce air resistance (drag), which is a force that opposes motion. By reducing the area exposed to the air, less resistive force acts on the cyclist, allowing them to ride faster with the same effort.
Key Points:
- Air resistance opposes the motion of moving objects.
- Bending forward reduces drag.
- Less air resistance helps improve speed and efficiency.
Real-Life Example:
Professional cyclists and motorcycle racers lean forward to reduce air resistance during races.
✅ Correct Answer: C. To reduce air resistance
7. What happens to acceleration if mass increases but force remains constant?
According to Newton’s Second Law of Motion, acceleration is inversely proportional to mass when the applied force remains constant. Therefore, increasing the mass of an object decreases its acceleration.
Key Points:
- Newton’s Second Law: F = ma.
- For constant force, greater mass results in lower acceleration.
- Lighter objects accelerate more easily than heavier ones.
Real-Life Example:
An empty cart accelerates faster than a loaded cart when pushed with the same force.
✅ Correct Answer: B. Decreases
8. When two objects interact, the forces between them are:
According to Newton’s Third Law of Motion, whenever one object exerts a force on another, the second object exerts an equal force in the opposite direction. These action and reaction forces always occur together and act on different objects.
Key Points:
- Action and reaction forces are equal in magnitude.
- They act in opposite directions.
- They always act on different objects.
Real-Life Example:
When you push against a wall, the wall pushes back on you with an equal and opposite force.
✅ Correct Answer: C. Equal and opposite
9. Why is it difficult to stop a moving truck compared to a bicycle?
A moving truck has much greater mass than a bicycle. Since momentum depends on both mass and velocity, the truck has greater momentum and requires a larger force or more time to stop.
Key Points:
- Momentum = Mass × Velocity.
- Greater mass means greater momentum.
- More momentum requires more force to stop.
Real-Life Example:
Heavy vehicles such as trucks need a longer braking distance than bicycles or motorcycles.
✅ Correct Answer: A. More momentum
10. Which quantity is affected by both direction and magnitude?
Velocity is a vector quantity because it has both magnitude (speed) and direction. If either the speed or the direction changes, the velocity also changes.
Key Points:
- Velocity is a vector quantity.
- It depends on both speed and direction.
- Distance, speed, and time are scalar quantities.
Real-Life Example:
A car moving at 60 km/h towards the north has a different velocity if it changes direction to the east, even if its speed remains the same.
✅ Correct Answer: C. Velocity
11. When a force is applied, which of the following may change?
When a force acts on an object, it can change the object’s shape, speed, or direction of motion. Depending on the magnitude and direction of the applied force, one or more of these changes may occur. This is one of the fundamental effects of force studied in Newton’s Laws of Motion.
Key Points:
- Force can change the shape of an object.
- Force can increase or decrease speed.
- Force can change the direction of motion.
Real-Life Example:
Kicking a football changes its speed and direction, while squeezing a sponge changes its shape.
✅ Correct Answer: D. All of these
12. Why do passengers in a car wear seat belts?
Seat belts protect passengers from the effects of inertia during sudden stops or collisions. While the car stops abruptly, the passenger’s body tends to continue moving forward due to Newton’s First Law of Motion. A seat belt provides the necessary external force to safely stop the passenger.
Key Points:
- Based on Newton’s First Law of Motion.
- Inertia causes the body to continue moving forward.
- Seat belts reduce the risk of injury during sudden braking.
Real-Life Example:
Seat belts prevent passengers from being thrown forward during a sudden stop or accident.
✅ Correct Answer: B. To prevent inertia effect
13. A ball rolling on the ground stops due to:
A rolling ball eventually stops because friction acts between the ball and the ground. Friction is a force that opposes motion and gradually reduces the ball’s speed until it comes to rest.
Key Points:
- Friction opposes the motion of objects.
- It slows down moving objects.
- Without friction, the ball would continue moving for a much longer time.
Real-Life Example:
A football kicked across a field gradually slows down and stops because of friction with the ground.
✅ Correct Answer: C. Friction
14. Which law explains the working of a jet engine?
A jet engine works on Newton’s Third Law of Motion, which states that for every action, there is an equal and opposite reaction. The engine pushes hot gases backward, and in return, the gases push the aircraft forward with an equal and opposite force.
Key Points:
- Newton’s Third Law is the action-reaction law.
- Action and reaction forces act on different objects.
- Jet propulsion is a practical application of this law.
Real-Life Example:
Rockets and jet aircraft move forward by expelling gases backward.
✅ Correct Answer: A. Third Law
15. If a force acts in the same direction as the object’s motion, the object will:
When a force acts in the same direction as an object’s motion, it increases the object’s velocity, causing it to speed up. According to Newton’s Second Law of Motion, a net force produces acceleration in the direction of the applied force.
Key Points:
- Force in the direction of motion increases speed.
- Acceleration occurs in the direction of the net force.
- Newton’s Second Law explains this relationship.
Real-Life Example:
A cyclist pedals harder in the direction of travel to increase speed.
✅ Correct Answer: D. Speed up
16. Which of the following is a vector quantity?
Velocity is a vector quantity because it has both magnitude and direction. Unlike scalar quantities such as distance, speed, and time, velocity changes if either the speed or the direction of an object changes.
Key Points:
- Velocity has both magnitude and direction.
- It is a vector quantity.
- Distance, speed, and time are scalar quantities.
Real-Life Example:
A car moving at 60 km/h towards the north has a different velocity if it changes direction to the east, even though its speed remains the same.
✅ Correct Answer: C. Velocity
17. A body at rest will remain at rest unless:
According to Newton’s First Law of Motion, a body at rest remains at rest unless acted upon by an external unbalanced force. This property is due to inertia, which resists any change in the state of motion.
Key Points:
- Newton’s First Law is also called the Law of Inertia.
- An external unbalanced force is required to change the state of rest.
- Inertia resists changes in motion.
Real-Life Example:
A book lying on a table remains at rest until someone pushes or lifts it.
✅ Correct Answer: A. Force acts on it
18. Which factor affects inertia?
Inertia is the property of an object that resists changes in its state of motion. It depends only on the mass of the object. The greater the mass, the greater the inertia.
Key Points:
- Inertia depends only on mass.
- Greater mass means greater inertia.
- Inertia is independent of speed and force.
Real-Life Example:
It is easier to push an empty shopping cart than a fully loaded one because the loaded cart has greater inertia.
✅ Correct Answer: B. Mass
19. What is required to change the direction of a moving object?
Changing the direction of a moving object requires an external force. According to Newton’s Laws of Motion, an object continues moving in a straight line unless acted upon by an unbalanced force.
Key Points:
- Force is needed to change direction.
- A change in direction means a change in velocity.
- Unbalanced forces alter the motion of an object.
Real-Life Example:
A batsman changes the direction of a cricket ball by applying force with the bat.
✅ Correct Answer: D. Force
20. When force is removed, a moving object continues to move due to:
According to Newton’s First Law of Motion, a moving object continues in its state of motion unless acted upon by an external unbalanced force. This tendency to resist changes in motion is called inertia.
Key Points:
- Newton’s First Law explains inertia.
- Inertia keeps an object moving in the absence of an external force.
- Friction is the force that usually slows down moving objects.
Real-Life Example:
A hockey puck glides across a smooth ice surface for a long distance because very little friction acts on it.
✅ Correct Answer: C. Inertia
Final Revision Tips
- Remember Newton’s Three Laws of Motion and identify their real-life applications.
- Inertia depends only on mass—greater mass means greater inertia.
- Momentum = Mass × Velocity; increasing either mass or velocity increases momentum.
- Force = Mass × Acceleration (F = ma); for the same force, a lighter object accelerates more.
- Impulse = Force × Time and it changes an object’s momentum.
- Action and reaction forces are always equal in magnitude and opposite in direction.
- Velocity and momentum are vector quantities, while distance, speed, and time are scalar quantities.
- Friction and air resistance oppose motion and reduce the speed of moving objects.
- Seat belts, jet engines, and sudden braking are common real-life applications of Newton’s Laws.
- In TNPSC exams, concept-based and application-oriented questions are frequently asked from Laws of Motion.
Further Reading
To strengthen your understanding of Newton’s Laws of Motion, force, inertia, momentum, impulse, friction, and their real-life applications, read NCERT Class 11 Physics – Chapter 4: Laws of Motion. This chapter explains the fundamental principles of motion with clear examples and is an excellent resource for TNPSC and other competitive exam preparation.
