Class 9 Physics: Force and Law of Motion MCQ

Welcome to this comprehensive blog post dedicated to ‘Force and Law of Motion’. Through these multiple choice questions (MCQs), we aim to test and enhance your understanding of this critical topic in Physics. Let’s dive right in!

1. Which of the following is the correct definition of force?

a) The rate of change of momentum
b) A quantity that has only magnitude
c) A push or pull on an object
d) The rate of change of velocity

Answer:

c) A push or pull on an object

Explanation:

Force is defined as a push or a pull on an object. It has both magnitude and direction, making it a vector quantity.

2. Newton’s First Law of Motion is also known as?

a) Law of Inertia
b) Law of Gravitation
c) Law of Acceleration
d) Law of Conservation of Energy

Answer:

a) Law of Inertia

Explanation:

Newton’s First Law of Motion states that an object remains at rest or in uniform motion unless acted upon by an external force. This is commonly known as the Law of Inertia.

3. According to Newton’s Second Law of Motion, force is the product of:

a) Velocity and time
b) Mass and velocity
c) Mass and acceleration
d) Distance and time

Answer:

c) Mass and acceleration

Explanation:

Newton’s Second Law states that F=m×a, where F is the force, m is the mass, and a is the acceleration.

4. An object moving with a constant velocity has:

a) A constant force applied to it
b) No net force acting on it
c) An increasing force acting on it
d) A decreasing force acting on it

Answer:

b) No net force acting on it

Explanation:

If an object is moving with constant velocity, it implies there’s no net force acting on it. If there were, the object would accelerate.

5. The measure of the amount of matter in an object is:

a) Weight
b) Force
c) Mass
d) Density

Answer:

c) Mass

Explanation:

Mass is the measure of the amount of matter in an object. Weight is the gravitational force acting on a mass.

6. The SI unit of force is:

a) Joule
b) Newton
c) Pascal
d) Watt

Answer:

b) Newton

Explanation:

The SI unit of force is Newton (N), which is defined as the force required to accelerate a one-kilogram mass by one meter per second squared.

7. When two equal and opposite forces act on a body, they:

a) Cancel each other out
b) Produce rotational motion
c) Increase the net force on the body
d) Cause the body to move in a straight line

Answer:

a) Cancel each other out

Explanation:

Two equal and opposite forces are termed as balanced forces. They cancel out each other’s effects, leading to no net force acting on the body.

8. Inertia is directly proportional to:

a) Acceleration
b) Force
c) Velocity
d) Mass

Answer:

d) Mass

Explanation:

Inertia is the tendency of an object to resist a change in motion. This tendency is directly proportional to the mass of the object.

9. Which of Newton’s laws explains why a passenger in a car tends to lean forward when the car suddenly stops?

a) First Law
b) Second Law
c) Third Law
d) Law of Gravitation

Answer:

a) First Law

Explanation:

Newton’s First Law, or the Law of Inertia, explains that objects in motion want to stay in motion. When a car stops, the passenger’s body wants to continue its forward motion, causing the lean.

10. What does Newton’s Third Law of Motion state?

a) Every action has an equal and opposite reaction.
b) Force is equal to mass times acceleration.
c) Objects at rest tend to stay at rest.
d) Force is inversely proportional to acceleration.

Answer:

a) Every action has an equal and opposite reaction.

Explanation:

Newton’s Third Law of Motion states that for every action, there’s an equal and opposite reaction. This means forces always come in pairs.

11. The gravitational force between two objects will increase if:

a) The distance between them decreases
b) The masses of both objects decrease
c) The speed of one object increases
d) They are made of different materials

Answer:

a) The distance between them decreases

Explanation:

According to Newton’s law of universal gravitation, the gravitational force between two objects is inversely proportional to the square of the distance between their centers.

12. An object moving in a circular path with a constant speed is:

a) In equilibrium
b) Not accelerating
c) Experiencing a net force towards the center
d) Not under the influence of any force

Answer:

c) Experiencing a net force towards the center

Explanation:

This force is known as centripetal force. Even if the speed is constant, there’s a change in direction, indicating acceleration.

13. A 2 kg object is accelerating at 3 m/s^2. What is the net force acting on it?

a) 0.67 N
b) 5 N
c) 6 N
d) 8 N

Answer:

c) 6 N

Explanation:

Using Newton’s second law, F=m×a. So, F=2 kg ×3 m/s^2 =6 N.

14. Which of the following is a contact force?

a) Magnetic force
b) Gravitational force
c) Frictional force
d) Electrical force

Answer:

c) Frictional force

Explanation:

Frictional force acts when two surfaces are in contact. It opposes the motion of one object sliding or trying to slide over another.

15. A car is moving to the right and suddenly stops. The passengers inside the car will:

a) Move to the right
b) Move to the left
c) Stay at the same spot
d) Move upwards

Answer:

a) Move to the right

Explanation:

Due to inertia, the passengers inside the car will continue in their state of motion (to the right) when the car suddenly stops.

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