Impulse Class 11 Physics Notes | NEET & CBSE Complete Guide

Impulse and Momentum Class 11 | Definition, Formula, MCQs & Notes

Impulse explained using a cricket ball collision and force-time relation showing change in momentum.

- Dr.Sanjaykumar Pawar 

 IMPULSE

│

├── Introduction

│   │

│   ├── Large force may act for a very short time

│   ├── Such force can produce a noticeable change in momentum

│   └── This effect is studied using the concept of impulse

│

├── Example: Ball Hits a Wall

│   │

│   ├── Ball moves towards the wall

│   ├── Ball comes in contact with the wall

│   ├── Contact time is very short

│   ├── Wall exerts a large force on the ball

│   ├── Ball bounces back

│   └── Momentum changes direction

│

├── Need for Impulse

│   │

│   ├── Exact force is difficult to measure

│   ├── Exact contact time is difficult to measure

│   ├── Product of force and time can be measured

│   └── This product is called impulse

│

├── Definition of Impulse

│   │

│   ├── Impulse = Force × Time Duration

│   ├── Symbol: J

│   └── J = FΔt

│

├── Relation with Momentum

│   │

│   ├── Newton's Second Law

│   │   └── F = Δp/Δt

│   │

│   ├── Multiplying by Δt

│   │   └── FΔt = Δp

│   │

│   └── Therefore

│       └── Impulse = Change in Momentum

│

├── Formula

│   │

│   ├── J = FΔt

│   ├── J = Δp

│   └── J = pf − pi

│

├── SI Unit

│   │

│   ├── Newton-second (N·s)

│   ├── kg·m·s⁻¹

│   └── Same as momentum unit

│

├── Impulsive Force

│   │

│   ├── Very large force

│   ├── Acts for a very short duration

│   ├── Produces finite change in momentum

│   └── Called impulsive force

│

├── Characteristics of Impulsive Force

│   │

│   ├── High magnitude

│   ├── Short time interval

│   ├── Sudden action

│   └── Causes significant momentum change

│

├── Examples of Impulsive Force

│   │

│   ├── Bat hitting a cricket ball

│   ├── Football being kicked

│   ├── Hammer striking a nail

│   ├── Bullet hitting a target

│   └── Ball bouncing from a wall

│

├── Newtonian View

│   │

│   ├── Earlier treated separately

│   ├── Modern mechanics makes no distinction

│   ├── Impulsive force is an ordinary force

│   └── Difference:

│       ├── Very large magnitude

│       └── Very short duration

│

└── NEET Quick Revision

    │

    ├── Impulse = Force × Time

    ├── Impulse = Change in Momentum

    ├── J = FΔt = Δp

    ├── Unit = N·s

    ├── Impulsive force → Large force + Short time

    └── Key Examples:

        ├── Bat–Ball

        ├── Hammer–Nail

        ├── Bullet–Target

        └── Ball–Wall

Impulse (NEET Level Notes)

1. What is Impulse?

Sometimes a very large force acts on a body for a very short duration of time. Even though the time interval is small, the momentum of the body changes significantly. The effect produced by such a force is called Impulse.

Impulse is the product of force and the time interval for which it acts.

2. Example: Ball Striking a Wall

• Consider a ball moving towards a wall.
• When the ball hits the wall, contact lasts for a very short time.
• During this short interval, the wall exerts a large force on the ball.
• The ball bounces back in the opposite direction.
• Therefore, its momentum changes.

Although the force and contact time are difficult to measure separately, their product can be measured easily.

3. Definition of Impulse

Impulse = Force × Time Duration

J = FΔt

Where:

• J = Impulse
• F = Force
• Δt = Time interval

4. Relation Between Impulse and Momentum

According to Newton's Second Law of Motion:

F = Δp / Δt

Multiplying both sides by Δt:

FΔt = Δp

Therefore,

Impulse = Change in Momentum

J = Δp = pf − pi

Where:

• pf = Final Momentum
• pi = Initial Momentum

5. SI Unit of Impulse

Since:

Impulse = Force × Time

SI Unit:

Newton-second (N·s)

Since impulse equals change in momentum, it can also be written as:

kg·m/s

6. Impulsive Force

A large force acting for a very short time and producing a finite change in momentum is called an Impulsive Force.

7. Characteristics of Impulsive Force

• Very large magnitude.
• Acts for a very short duration.
• Produces a noticeable change in momentum.
• Can change speed, direction, or both.

8. Examples of Impulsive Forces

• Bat hitting a cricket ball.
• Football being kicked.
• Hammer striking a nail.
• Bullet hitting a target.
• Ball bouncing from a wall.

9. Important Concept

In earlier days, impulsive forces were treated as different from ordinary forces. However, according to Newtonian Mechanics, there is no special distinction.

An impulsive force is simply an ordinary force that is very large and acts for a very short interval of time.

NEET Quick Revision

• Impulse = Force × Time
• Impulse = Change in Momentum
• Formula: J = FΔt = Δp
• SI Unit: N·s or kg·m/s
• Impulsive Force: Large force acting for a short time.
• Examples: Bat-ball collision, hammer-nail, bullet-target, ball-wall collision.

NEET Definition: Impulse is the product of force and the time interval for which it acts, and it is equal to the change in momentum of the body.

CBSE Class 11 Physics – Impulse and Impulsive Force Question Bank with Answers

A. Multiple Choice Questions (MCQs)

1. Impulse is equal to:

a) Force × Velocity
b) Force × Time
c) Mass × Velocity
d) Work Done

Answer: (b) Force × Time

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2. The SI unit of impulse is:

a) Newton
b) Joule
c) Newton-second
d) Watt

Answer: (c) Newton-second

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3. Impulse is equal to:

a) Change in velocity
b) Change in force
c) Change in momentum
d) Change in acceleration

Answer: (c) Change in momentum

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4. An impulsive force acts for:

a) Long duration
b) Infinite duration
c) Very short duration
d) Zero duration

Answer: (c) Very short duration

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5. Which of the following is an example of impulsive force?

a) Gravitational force
b) Frictional force
c) Bat hitting a ball
d) Magnetic force

Answer: (c) Bat hitting a ball

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6. If force doubles and time halves, impulse becomes:

a) Double
b) Half
c) Same
d) Zero

Answer: (c) Same

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7. The dimension of impulse is:

a) [MLT^-1]
b) [ML²T^-2]
c) [MLT^-2]
d) [M⁰LT^-1]

Answer: (a) [MLT^-1]

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8. Impulse-momentum theorem is based on:

a) Newton's First Law
b) Newton's Second Law
c) Newton's Third Law
d) Law of Gravitation

Answer: (b) Newton's Second Law

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9. A force of 20 N acts for 5 s. Impulse is:

a) 4 Ns
b) 25 Ns
c) 100 Ns
d) 200 Ns

Answer: (c) 100 Ns

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10. Impulse has the same unit as:

a) Energy
b) Work
c) Momentum
d) Power

Answer: (c) Momentum

B. Very Short Answer Questions (1 Mark)

1. Define impulse.

Answer: Impulse is the product of force and the time interval for which it acts.

2. Write the formula for impulse.

Answer: J = FΔt

3. State the SI unit of impulse.

Answer: Newton-second (N·s).

4. What is impulsive force?

Answer: A large force acting for a very short time is called an impulsive force.

5. What physical quantity does impulse change?

Answer: Momentum.

C. Short Answer Questions (2–3 Marks)

1. Show that impulse equals change in momentum.

Answer:
From Newton's second law,
F = Δp/Δt

Multiplying by Δt,
FΔt = Δp

Therefore,
Impulse = Change in Momentum

2. Why is a batsman allowed to move his hands backward while catching a ball?

Answer: Moving the hands backward increases the time of impact. Since impulse remains constant, force decreases. Therefore, the catch becomes easier and safer.

3. Give three examples of impulsive force.

Answer:

1. Bat striking a cricket ball.
2. Hammer striking a nail.
3. Bullet hitting a target.

4. Write any two characteristics of impulsive force.

Answer:

1. It has a very large magnitude.
2. It acts for a very short duration.

5. Why does a karate player break bricks with a quick blow?

Answer: The hand applies a large force for a very short duration, producing a large impulse that breaks the bricks.

D. Long Answer Questions (5 Marks)

1. Define impulse and derive the relation between impulse and momentum.

Answer:

Impulse is the product of force and the time interval during which it acts.

Impulse = Force × Time

According to Newton's Second Law,
F = Δp/Δt

Multiplying both sides by Δt,
FΔt = Δp

Therefore,
Impulse = Change in Momentum

J = FΔt = Δp

The SI unit of impulse is Newton-second (N·s).

2. Explain impulsive force with examples.

Answer:

An impulsive force is a large force acting for a very short duration producing a finite change in momentum.

Characteristics:

1. Large magnitude.
2. Short duration.
3. Produces considerable change in momentum.

Examples:

• Bat hitting a ball.
• Hammer striking a nail.
• Bullet striking a target.
• Ball rebounding from a wall.

E. Assertion and Reason Questions

1. Assertion (A): Impulse is equal to change in momentum.
Reason (R): Newton's second law leads to the relation FΔt = Δp.

Answer: Both A and R are true and R is the correct explanation of A.

2. Assertion (A): Impulsive force acts for a long time.
Reason (R): Impulsive force is very large in magnitude.

Answer: A is false but R is true.

3. Assertion (A): Impulse has the same unit as momentum.
Reason (R): Impulse equals change in momentum.

Answer: Both A and R are true and R correctly explains A.

4. Assertion (A): Catching a ball with rigid hands is safer.
Reason (R): Force decreases when contact time increases.

Answer: A is false but R is true.

F. Fill in the Blanks

1. Impulse is the product of Force and time.
2. Impulse is equal to change in Momentum.
3. SI unit of impulse is Newton-second.
4. A large force acting for a short time is called an Impulsive force.
5. Impulse and momentum have the same Unit.
6. Bat striking a ball is an example of Impulsive force.
7. Impulse is represented by the symbol J.
8. Impulsive force acts for a very Short duration.

G. Statement-Based Questions (True/False)

1. Impulse equals force divided by time. — False
2. Impulse equals force multiplied by time. — True
3. Momentum changes when impulse acts. — True
4. Impulsive force acts for a long duration. — False
5. Newton-second is the SI unit of impulse. — True
6. A hammer striking a nail is an example of impulsive force. — True
7. Impulse and work have the same unit. — False
8. Impulse can change the direction of motion. — True

H. Match the Following

Column A	Column B
1. Impulse	a. Change in momentum
2. N·s	b. Unit of impulse
3. Bat hitting ball	c. Impulsive force
4. FΔt	d. Impulse formula

Answers:
1 → a
2 → b
3 → c
4 → d

I. Case Study Questions

Case Study 1

A cricket player catches a fast-moving ball by moving his hands backward while catching it.

1. Why does the player move his hands backward?

Answer: To increase the time of impact.

2. What happens to the force when impact time increases?

Answer: Force decreases.

3. Which concept explains this phenomenon?

Answer: Impulse.

4. What remains constant during catching?

Answer: Change in momentum (Impulse).

Case Study 2

A hammer strikes a nail for a very short time and drives it into a wooden block.

1. What type of force acts on the nail?

Answer: Impulsive force.

2. Why is the force called impulsive?

Answer: It is very large and acts for a very short time.

3. What quantity changes due to impulse?

Answer: Momentum.

4. State the formula of impulse.

Answer: J = FΔt

Important CBSE Exam Definitions

Impulse:
The product of force and time interval during which it acts is called impulse.

Impulsive Force:
A large force acting for a very short duration producing a finite change in momentum is called an impulsive force.

Impulse-Momentum Theorem:
Impulse acting on a body is equal to the change in momentum of the body.