Class 9 Exam Preparation

Laws of Motion: 50 Important MCQs

Revise Newton's laws, inertia, force, momentum and conservation of momentum through a complete interactive practice quiz with answers and explanations.

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Select one option for each question. Your progress is saved only while this page remains open. After attempting the quiz, select Check My Score to see your result and explanations. You can also reveal all answers for revision.

Quick revision formulas

Remember these four relations before beginning the MCQs.

p = mvMomentum

F = maForce for constant mass

F = Δp/ΔtRate of change of momentum

m₁u₁ + m₂u₂ = m₁v₁ + m₂v₂Conservation of momentum

Interactive MCQ Quiz

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Question 1

The tendency of an object to resist any change in its state of rest or motion is called:

A Momentum B Inertia C Acceleration D Impulse

Answer: B. Inertia is the property of matter that resists a change in its state of motion.

Question 2

The SI unit of force is:

A Joule B Pascal C Newton D Watt

Answer: C. Force is measured in newtons, written as N.

Question 3

Newton's First Law of Motion is also known as the:

A Law of gravitation B Law of inertia C Law of acceleration D Law of momentum

Answer: B. The first law explains inertia and the effect of balanced and unbalanced forces.

Question 4

The momentum of an object is given by:

A p = m/v B p = mv C p = ma D p = v/m

Answer: B. Momentum is the product of mass and velocity.

Question 5

The SI unit of momentum is:

A kg m/s B N/m C kg m/s² D N s²

Answer: A. Momentum has the SI unit kilogram metre per second.

Question 6

According to Newton's Second Law, force is proportional to the:

A Mass only B Velocity only C Rate of change of momentum D Distance travelled

Answer: C. Newton's second law connects force with the rate of change of momentum.

Question 7

For a body of constant mass, Newton's Second Law can be written as:

A F = mv B F = ma C F = m/a D F = av

Answer: B. For constant mass, the net force equals mass multiplied by acceleration.

Question 8

The mass of an object is a measure of its:

A Speed B Inertia C Acceleration D Weight only

Answer: B. Greater mass means greater resistance to a change in motion.

Question 9

Seat belts protect passengers mainly because they prevent injury caused by:

A Inertia of motion B Inertia of rest C Friction only D Gravity only

Answer: A. When a car stops suddenly, the passenger's body tends to keep moving forward.

Question 10

When a stationary bus starts suddenly, passengers tend to fall backward because of:

A Inertia of rest B Inertia of motion C Action and reaction D Conservation of energy

Answer: A. The lower body moves with the bus while the upper body tends to remain at rest.

Question 11

When a moving bus stops suddenly, passengers tend to move forward because of:

A Inertia of rest B Inertia of motion C Balanced force D Gravitational force

Answer: B. The body tends to continue moving even after the bus slows down.

Question 12

In the coin-and-card experiment, the coin falls into the glass when the card is flicked because the coin has:

A Inertia of rest B Inertia of motion C High acceleration D Zero mass

Answer: A. The coin tends to remain at rest while the card moves away quickly.

Question 13

Action and reaction forces always act on:

A The same object B Different objects C Only moving objects D Only stationary objects

Answer: B. The two forces are equal and opposite but act on different bodies.

Question 14

According to Newton's Third Law, action and reaction are:

A Equal and in the same direction B Unequal and opposite C Equal and opposite D Always balanced on one body

Answer: C. Every action has an equal and opposite reaction.

Question 15

While walking, a person moves forward because the ground exerts a force:

A Backward on the person B Forward on the person C Upward only D Downward only

Answer: B. The foot pushes the ground backward, and the ground pushes the person forward.

Question 16

A rocket moves upward because it:

A Pulls the air downward B Throws gases downward C Has no weight D Uses balanced forces

Answer: B. The backward ejection of gases produces an equal and opposite force on the rocket.

Question 17

The recoil of a gun is explained by:

A Newton's First Law only B Newton's Third Law C Law of gravitation D Balanced forces

Answer: B. The bullet moves forward and the gun experiences an equal and opposite force.

Question 18

The total momentum of an isolated system remains constant. This is the law of:

A Conservation of mass B Conservation of momentum C Conservation of speed D Conservation of force

Answer: B. If no external force acts, total momentum before and after an interaction remains the same.

Question 19

A 2 kg object moves at 3 m/s. Its momentum is:

A 1.5 kg m/s B 5 kg m/s C 6 kg m/s D 9 kg m/s

Answer: C. p = mv = 2 × 3 = 6 kg m/s.

Question 20

A 5 kg object accelerates at 2 m/s². The net force is:

A 2.5 N B 7 N C 10 N D 25 N

Answer: C. F = ma = 5 × 2 = 10 N.

Question 21

A force of 10 N acts on a 2 kg object. Its acceleration is:

A 2 m/s² B 5 m/s² C 10 m/s² D 20 m/s²

Answer: B. a = F/m = 10/2 = 5 m/s².

Question 22

A 3 kg object initially at rest is acted upon by a force of 6 N for 2 s. Its final speed is:

A 2 m/s B 4 m/s C 6 m/s D 12 m/s

Answer: B. a = 6/3 = 2 m/s² and v = u + at = 0 + 2 × 2 = 4 m/s.

Question 23

Impulse is equal to the:

A Change in momentum B Mass divided by velocity C Force divided by time D Acceleration divided by mass

Answer: A. Impulse equals force multiplied by time and is equal to the change in momentum.

Question 24

The same force is applied to two objects of different masses. The object with smaller mass gets:

A Smaller acceleration B Greater acceleration C The same acceleration D Zero acceleration

Answer: B. From a = F/m, acceleration is greater when mass is smaller.

Question 25

An unbalanced force can change an object's:

A State of motion B Mass C Chemical composition D Volume only

Answer: A. An unbalanced force can change speed, direction, or both.

Question 26

Balanced forces acting on an object produce:

A A change in momentum B No change in its state of motion C A large acceleration D A change in mass

Answer: B. Balanced forces have zero resultant force, so they do not change the state of motion.

Question 27

Friction usually acts:

A In the direction of motion B Opposite to relative motion C Vertically upward only D Toward the centre of Earth

Answer: B. Friction opposes relative motion or the tendency of motion between surfaces.

Question 28

A 20 kg cart moves at 0.5 m/s. Its momentum is:

A 10 kg m/s B 20 kg m/s C 40 kg m/s D 0.025 kg m/s

Answer: A. p = 20 × 0.5 = 10 kg m/s.

Question 29

A 1000 kg car moves at 10 m/s. Its momentum is:

A 100 kg m/s B 1000 kg m/s C 10,000 kg m/s D 100,000 kg m/s

Answer: C. p = 1000 × 10 = 10,000 kg m/s.

Question 30

A 0.1 kg ball moves at 20 m/s. Its momentum is:

A 0.5 kg m/s B 2 kg m/s C 20 kg m/s D 200 kg m/s

Answer: B. p = 0.1 × 20 = 2 kg m/s.

Question 31

During a collision in an isolated system, the total momentum:

A Always increases B Always decreases C Remains conserved D Becomes zero

Answer: C. Internal forces may change individual momenta, but total momentum remains constant.

Question 32

Action and reaction forces do not cancel each other because they:

A Are unequal B Act at different times C Act on different objects D Move in the same direction

Answer: C. Forces can cancel only when they act on the same object.

Question 33

A swimmer moves forward by pushing water backward. This illustrates:

A Newton's First Law B Newton's Third Law C Only friction D Conservation of mass

Answer: B. Water pushes the swimmer forward with an equal and opposite force.

Question 34

A horse can pull a cart forward mainly because:

A The cart pushes the horse forward B The ground exerts a forward frictional force on the horse C The horse has no inertia D Action and reaction cancel on the horse

Answer: B. The horse pushes the ground backward, and the ground pushes the horse forward.

Question 35

Dust comes out of a carpet when it is beaten because of:

A Inertia of rest B Inertia of motion C Gravity alone D Momentum conservation only

Answer: A. The carpet moves suddenly, while dust particles tend to remain at rest.

Question 36

Ripe fruits may fall when a tree branch is shaken because of:

A Inertia of rest B Inertia of direction C Balanced forces D Zero momentum

Answer: A. The branch moves suddenly, while the fruit tends to remain in its original state.

Question 37

When a car turns sharply, passengers lean outward because their bodies tend to:

A Move toward the centre B Continue in a straight line C Stop immediately D Lose mass

Answer: B. Inertia of direction makes the body tend to continue along the original straight path.

Question 38

If no net external force acts on a moving object, it will:

A Stop after some time in every case B Move with constant velocity C Speed up continuously D Move in a circle

Answer: B. With zero net force, acceleration is zero and velocity remains constant.

Question 39

Momentum is a:

A Scalar quantity B Vector quantity C Dimensionless quantity D Unitless quantity

Answer: B. Momentum has both magnitude and direction.

Question 40

Force is a:

A Scalar quantity B Vector quantity C Dimensionless quantity D Constant quantity

Answer: B. Force has magnitude as well as direction.

Question 41

The acceleration of an object is in the direction of the:

A Velocity always B Net force C Mass D Momentum always

Answer: B. Acceleration is produced in the direction of the resultant force.

Question 42

An 8 kg object moves at 4 m/s. Its momentum is:

A 2 kg m/s B 12 kg m/s C 32 kg m/s D 64 kg m/s

Answer: C. p = 8 × 4 = 32 kg m/s.

Question 43

A 2 kg body changes its velocity from 4 m/s to 10 m/s in the same direction. The change in momentum is:

A 6 kg m/s B 8 kg m/s C 12 kg m/s D 20 kg m/s

Answer: C. Change in momentum = m(v - u) = 2(10 - 4) = 12 kg m/s.

Question 44

If the change in momentum is 12 kg m/s in 3 s, the average force is:

A 4 N B 9 N C 12 N D 36 N

Answer: A. Force = change in momentum/time = 12/3 = 4 N.

Question 45

A 0.5 kg object accelerates at 6 m/s². The force acting on it is:

A 0.083 N B 3 N C 6.5 N D 12 N

Answer: B. F = ma = 0.5 × 6 = 3 N.

Question 46

Which pair is an action-reaction pair?

A Weight of a book and normal force on the book B Earth pulls an apple and the apple pulls Earth C Friction and weight on a moving box D Two forces acting rightward on a cart

Answer: B. Earth and the apple exert equal and opposite gravitational forces on each other.

Question 47

Which pair is not an action-reaction pair?

A A hand pushes a wall and the wall pushes the hand B A swimmer pushes water and water pushes the swimmer C Weight of a book and normal force on the same book D A gun pushes a bullet and the bullet pushes the gun

Answer: C. Weight and normal force act on the same book, so they are not a third-law pair.

Question 48

A passenger seems to move left when a car suddenly turns right because of:

A Inertia of direction B Inertia of rest only C Gravity D Conservation of mass

Answer: A. The passenger's body tends to continue in its original straight-line direction.

Question 49

A cricketer pulls the hands backward while catching a fast ball to:

A Increase the force of impact B Decrease the stopping time C Increase the stopping time and reduce force D Increase the ball's momentum

Answer: C. For the same change in momentum, increasing stopping time reduces the average force.

Question 50

Airbags reduce injuries mainly because they:

A Increase stopping time B Increase momentum C Decrease passenger mass D Remove inertia

Answer: A. Airbags increase the time over which momentum changes, reducing the average force on the body.

Frequently Asked Questions

What are Newton's three laws of motion? +

The first law explains inertia, the second law relates force to the rate of change of momentum, and the third law states that every action has an equal and opposite reaction.

What is momentum in Class 9 physics? +

Momentum is the product of an object's mass and velocity. It is written as p = mv and its SI unit is kg m/s.

Why do passengers move forward when a bus stops? +

Their bodies tend to continue moving due to inertia of motion even when the bus slows down suddenly.

Do action and reaction forces cancel each other? +

No. They act on different objects, so they do not cancel each other on a single object.

How can I score better in Laws of Motion MCQs? +

Learn the concepts behind inertia, resultant force, momentum and action-reaction pairs. Then practise numerical questions using p = mv and F = ma.

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Laws of Motion Class 9: 50 Important MCQs with Answers