Practicing Class 9 Science MCQ and Class 9 Science Exploration Chapter 6 MCQ Online Test with Answers How Forces Affect Motion daily helps in time management.
Class 9 Science Chapter 6 How Forces Affect Motion MCQ
How Forces Affect Motion MCQ
Class 9 Science Chapter 6 MCQ online test
Question 1.
A net force acts on an object. Which of the following will definitely happen?
(a) Object will accelerate
(b) Object will stop moving
(c) Object will move in a straight line
(d) None of these
Answer:
(a) Object will accelerate
Question 2.
A book is lying at rest on a table. The forces acting on it are:
(a) Only gravity
(b) Only normal force
(c) Gravity and normal force both, balanced
(d) Gravity and normal force both, unbalanced
Answer:
(c) Gravity and normal force both, balanced
Question 3.
A force of 20 N acts on an object of mass 4 kg. The acceleration produced is:
(a) 80 m/s2
(b) 5 m/s2
(c) 0.2 m/s2
(d) 24 m/s2
Answer:
(b) 5 m/s2
Question 4.
According to Newton’s Third Law, when a horse pulls a cart forward, the cart:
(a) Exerts no force on the horse
(b) Exerts an equal force on the horse in the backward direction
(c) Exerts a smaller force on the horse
(d) Exerts a larger force on the horse
Answer:
(b) Exerts an equal force on the horse in the backward direction
Question 5.
An object is moving with uniform velocity on a frictionless surface. The net force acting on it is:
(a) In the direction of motion
(b) Equal to its weight
(c) Opposite to the direction of motion
(d) Zero
Answer:
(c) Opposite to the direction of motion
How Forces Affect Motion Class 9 Assertion and Reason Questions
Directions: For Questions number (i) to (ii), two statements are given — one labelled as Assertion (A) and the other labelled as Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below.
(a) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
(b) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
(c) Assertion (A) is true, but Reason (R) is false.
(d) Assertion (A) is false, but Reason (R) is true.
Question 1.
Assertion (A): A cricket fielder pulls their hands back while catching a fast ball.
Reason (R): Pulling the hands back increases the time of deceleration, which reduces the force experienced by the hands.
Answer:
(a) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
Explanation:
This is a direct application of Newton’s Second Law. Increasing the time of stopping reduces the deceleration (rate of change of velocity), and from F = ma, a smaller acceleration means a smaller force. This reduces the risk of injury.
Question 2.
Assertion (A): A rocket can move in outer space where there is no air.
Reason (R): A rocket works on the principle of Newton’s Third Law. It expels gases in one direction and the reaction force propels it in the opposite direction.
Answer:
(a) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
Explanation:
A rocket does not need air to push against. It expels exhaust gases downward from its engine. By Newton’s Third Law, these gases exert an equal and opposite force on the rocket upward, propelling it forward. This works perfectly in the vacuum of space.
How Forces Affect Motion Class 9 Fill in the Blanks
1. The SI unit of force is ___________.
Answer:
newton/N
2. Newton’s ___________ law of motion is also brown as the Law of Inertia.
Answer:
First
3. The force that opposes relative motion between two surfaces in contact is called ___________.
Answer:
friction
4. The mathematical expression for Newton’s Second Law is ___________.
Answer:
F = ma
5. Action and reaction forces in Newton’s Third Law always act on ___________ objects.
Answer:
two different
How Forces Affect Motion Class 9 True or False
1. Balanced forces can change the state of motion of an object.
Answer:
False.
Balanced forces produce zero net force. By Newton’s First Law, zero net force means no change in the state of motion. The object either remains at rest or continues with the same velocity.
2. The weight of an object depends on its mass.
Answer:
True.
Weight = mg. Since g is approximately constant near the Earth’s surface, weight is directly proportional to mass. A heavier object weighs more.
3. Newton’s Third Law applies only to contact forces.
Answer:
False.
Newton’s Third Law applies to all types of forces, including non-contact forces such as gravitational force, magnetic force, and electrostatic force. For example, the Earth and a fruit exert equal and opposite gravitational forces on each other.
4. An object at rest has no forces acting on it.
Answer:
False.
An object at rest may have many forces acting on it, but these forces are balanced (net force = zero). For example, a book on a table has gravity and normal force both acting on it.
5. If mass of an object is doubled and force is kept the same, acceleration becomes half.
Answer:
True.
From Newton’s Second Law, a = \(\frac{F}{m}\). If m is doubled and F remains constant, then a = \(\frac{F}{2 m}\), which is half the original acceleration.
How Forces Affect Motion Class 9 Match the Following
Question 1.
Match the type of force with the current situation.
| Column A (Type of force) | Column B (Current situation) |
| 1. Balanced Forces | (a) A book lying at rest on a table |
| 2. Unbalanced Forces | (b) A football moving and gradually stopping on ground |
| 3. Frictional Force | (c) A person pushing a wall but it does not move |
| 4. Muscular Force | (d) An apple falling from a tree |
| 5. Gravitational force | (e) A box starting to move when pushed harder |
Answer:
| Column A (Type of force) | Column B (Current situation) |
| 1. Balanced Forces | (a) A book lying at rest on a table |
| 2. Unbalanced Forces | (e) A box starting to move when pushed harder |
| 3. Frictional Force | (b) A football moving and gradually stopping on ground |
| 4. Muscular Force | (c) A person pushing a wall but it does not move |
| 5. Gravitational Force | (d) An apple falling from a tree |
Question 2.
Match the concept with its correct explanation.
| Column A (Type of force) | Column B (Current situation) |
| 1. Balanced Forces | (a) A book lying at rest on a table |
| 2. Unbalanced Forces | (e) A box starting to move when pushed harder |
| 3. Frictional Force | (b) A football moving and gradually stopping on ground |
| 4. Muscular Force | (c) A person pushing a wall but it does not move |
| 5. Gravitational Force | (d) An apple falling from a tree |
Answer:
| Column A (Concept) | Column B (Explanation) |
| 1. Inertia | (b) Resistance to change in state of motion |
| 2. Newton’s First Law | (d) A body remains at rest or uniform motion unless acted upon by external force |
| 3. Mass | (e) Measure of inertia of a body |
| 4. Force | (c) Push or pull that can change shape, speed or direction |
| 5. Momentum | (a) Product of mass and velocity |
MCQ On How Forces Affect Motion Class 9 for Practice
Choose the correct option in the following questions:
Question 1.
When two forces of 12 N and 5 N act on a body in opposite directions, the net force is:
(a) 17 N
(b) 7 N
(c) 60 N
(d) 2.4 N
Question 2.
A 3 kg object accelerates at 4 m/s2. The net force acting on it is
(a) 0.75 N
(b) 7N
(c) 9 N
(d) 1.33 N
Question 3.
Which of Newton’s laws is called the Law of Inertia?
(a) First
(b) Second
(c) Third
(d) All three
Question 4.
If you double both the force and the mass of an object, the acceleration
(a) Doubles
(b) Halves
(c) Remains the same
(d) Becomes zero
Question 5.
A person standing in a stationary lift feels lighter when the lift:
(a) Moves up at constant speed
(b) Moves down at constant speed
(c) Accelerates downward
(d) Accelerates upward
Assertion-Reason Questions
Directions: For Questions number (i) to (ii), two statements are given — one labelled as Assertion (A) and the other labelled as Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below.
(a) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
(b) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
(c) Assertion (A) is true, but Reason (R) is false.
(d) Assertion (A) is false, but Reason (R) is true.
Question 1.
Assertion (A): Passengers in a bus lurch forward when the bus stops suddenly.
Reason (R): This is because of the inertia of rest of the passengers.
Question 2.
Assertion (A): A gun recoils backward when fired.
Reason (R): By Newton’s Second Law, the force on the bullet produces an equal force on the gun.
Fill in the Blanks:
1. The tendency of an object to remain in its state of rest or uniform motion is called ___________.
2. The acceleration due to gravitational force by the Earth is approximately ___________ m/s2.
3. Newton’s Third Law states that action and reaction forces are always equal in ___________ and opposite in ___________.
4. For a system of two connected objects of masses m] and mv the acceleration under force F is given by ___________.
State whether the statements given below are True or False:
1. If the net force on an object is doubled, its acceleration becomes four times.
2. Newton’s Third Law forces always act on the same object.
3. The force of friction depends on the nature of the surfaces in contact.
4. A moving object on a frictionless surface needs no force to keep moving.
5. The weight of an object is the same everywhere on Earth’s surface.
Match the Columns:
Question 1.
Match the following items given in Column A with that in Column B.
| Column A | Column B |
| 1. Inertia | (d) Rocket propulsion |
| 2. Requires physical interaction | (b) Resistance to change in motion |
| 3. Equal and opposite forces | (c) Spring balance |
| 4. Measures force | (d) Contact force |
Question 2.
Match the following items given in Column A with that in Column B.
| Column A | Column B |
| 1. Walking on Earth | (a) Galileo Galilei |
| 2. Thought experiments on friction | (b) Results in 0 acceleration |
| 3. Balanced force | (c) Newton’s Third Law |
| 4. Cracking a coconut | (d) Large force in short time |