Retardation (Negative Acceleration) Practice Questions with Answers | CBSE Class 9 & NEET Physics Notes

 Dr Sanjay Kumar Pawar

Retardation (Negative Acceleration) Notes, MCQs & Numericals | CBSE & NEET 

Retardation (Negative Acceleration) explained with formulas, solved examples, and practice questions for CBSE Class 9 and NEET.

Internal Links

1. Motion in One Dimension Notes

2. Distance and Displacement Explained

3. Speed, Velocity and Acceleration Notes

4. Uniform and Non-Uniform Motion

5. Equations of Motion with Derivations

6. Graphs of Motion (Distance-Time & Velocity-Time)

7. Newton's Laws of Motion

8. Force and Inertia Notes

9. Work, Energy and Power

10. Gravitation Notes

11. Units and Measurements

12. Scalars and Vectors

13. Physics Formula Sheet for Class 9

14. CBSE Class 9 Science Chapter-wise Notes

15. NEET Foundation Physics Practice Questions

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Retardation (Negative Acceleration)

CBSE | NCERT | NEET Foundation

Very Short Answer Questions (1 Mark)

1. What is retardation?
   Retardation is the decrease in velocity of a moving body with time. It is also called negative acceleration.
2. What is another name for negative acceleration?
   Deceleration or Retardation.
3. What is the SI unit of retardation?
   m/s²
4. Can acceleration be negative?
   Yes. Negative acceleration is called retardation.
5. A vehicle slows down. What is the sign of acceleration?
   Negative (−)
6. What is the final velocity of a body that comes to rest?
   0 m/s
7. Which equation of motion is used when time is not given?
   v² = u² + 2as
8. What happens to the speed during retardation?
   The speed decreases.
9. What is the SI unit of velocity?
   m/s
10. What is the SI unit of displacement?
    metre (m)

Short Answer Questions (2 Marks)

Q1. Differentiate between Acceleration and Retardation

Acceleration	Retardation
Speed increases	Speed decreases
Positive	Negative
Velocity increases	Velocity decreases

Q2. Write the three equations of motion.

v = u + at

s = ut + ½at²

v² = u² + 2as

Q3. Write the equations for retardation.

v = u − at

s = ut − ½at²

v² = u² − 2as

Solved Numerical Questions (3 Marks)

Question 1

A bike moves with an initial velocity of 20 m/s. It stops after 5 seconds. Find its retardation.

Given
u = 20 m/s
v = 0 m/s
t = 5 s

v = u + at

0 = 20 + 5a

5a = -20

a = -4 m/s²

Retardation = 4 m/s²

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Question 2

A car moving at 30 m/s comes to rest in 6 seconds. Find the retardation.

Given
u = 30 m/s
v = 0 m/s
t = 6 s

v = u + at

0 = 30 + 6a

6a = -30

a = -5 m/s²

Retardation = 5 m/s²

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Question 3

A train slows down from 40 m/s to 20 m/s in 10 seconds. Find the acceleration.

Given
u = 40 m/s
v = 20 m/s
t = 10 s

v = u + at

20 = 40 + 10a

10a = -20

a = -2 m/s²

Retardation = 2 m/s²

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Question 4

A bus moving at 25 m/s stops after travelling 125 m. Find the retardation.

Given
u = 25 m/s
v = 0 m/s
s = 125 m

v² = u² + 2as

0 = 25² + 2 × a × 125

0 = 625 + 250a

250a = -625

a = -2.5 m/s²

Retardation = 2.5 m/s²

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Question 5

A car moving at 15 m/s stops after travelling 45 m. Find the retardation.

Given
u = 15 m/s
v = 0 m/s
s = 45 m

v² = u² + 2as

0 = 15² + 2 × a × 45

0 = 225 + 90a

90a = -225

a = -2.5 m/s²

Retardation = 2.5 m/s²

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Question 6

A scooter slows from 18 m/s to 6 m/s in 4 seconds. Find the retardation.

a = (6 − 18) / 4

a = -3 m/s²

Retardation = 3 m/s²

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Question 7

A train moving at 72 m/s stops in 12 seconds. Find the retardation.

a = (0 − 72) / 12

a = -6 m/s²

Retardation = 6 m/s²

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Question 8

A bus slows from 50 m/s to 20 m/s in 10 seconds. Find the retardation.

a = (20 − 50) / 10

a = -3 m/s²

Retardation = 3 m/s²

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Question 9

A car moving at 10 m/s stops in 2 seconds. Find the retardation.

a = (0 − 10) / 2

a = -5 m/s²

Retardation = 5 m/s²

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Question 10

A truck moving at 36 m/s comes to rest in 9 seconds. Find the retardation.

a = (0 − 36) / 9

a = -4 m/s²

Retardation = 4 m/s²

Multiple Choice Questions (MCQs)

1. Retardation is also called

A. Positive Acceleration
B. Uniform Motion
C. Negative Acceleration
D. Velocity

Answer: C. Negative Acceleration

2. SI unit of acceleration is

A. metre
B. second
C. m/s²
D. km/h

Answer: C. m/s²

3. When brakes are applied, acceleration becomes

A. Positive
B. Zero
C. Negative
D. Infinite

Answer: C. Negative

4. Which equation is used when time is not given?

A. v = u + at
B. s = ut
C. v² = u² + 2as
D. a = v/t

Answer: C. v² = u² + 2as

5. Final velocity of a body at rest is

A. 5 m/s
B. 10 m/s
C. 0 m/s
D. 100 m/s

Answer: C. 0 m/s

6. Retardation decreases

A. Time
B. Velocity
C. Distance
D. Mass

Answer: B. Velocity

7. Initial velocity is represented by

A. v
B. s
C. u
D. t

Answer: C. u

8. Final velocity is represented by

A. u
B. a
C. s
D. v

Answer: D. v

9. Time is represented by

A. a
B. t
C. s
D. u

Answer: B. t

10. Displacement is represented by

A. s
B. a
C. u
D. v

Answer: A. s

Higher Order Thinking Questions (HOTS)

Q1. Why is retardation called negative acceleration?

Retardation acts opposite to the direction of motion and decreases the velocity of a moving body. Therefore, its value is negative.

Q2. Can a body move forward while having negative acceleration?

Yes. If a moving body slows down while still moving forward, it has negative acceleration (retardation).

Assertion and Reason

Question 1

Assertion (A): Retardation decreases the speed of a moving body.

Reason (R): Retardation acts opposite to the direction of motion.

Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

Question 2

Assertion (A): A car moving at constant speed has retardation.

Reason (R): Constant speed means acceleration is zero.

Assertion is false, but Reason is true.

Case Study Question

A car is moving with an initial velocity of 60 m/s. The driver applies brakes and the car stops after travelling 180 m.

Questions

1. What is the initial velocity?
2. What is the final velocity?
3. Which equation of motion will be used?
4. Find the retardation.

Answers

Initial Velocity = 60 m/s

Final Velocity = 0 m/s

Formula Used:

v² = u² + 2as

0 = 60² + 2 × a × 180

0 = 3600 + 360a

360a = -3600

a = -10 m/s²

Retardation = 10 m/s²

Quick Revision

v = u + at

s = ut + ½at²

v² = u² + 2as

For Retardation

v = u − at

s = ut − ½at²

v² = u² − 2as

Exam Tips

• Always write the SI unit in the final answer.
• Write: Given → Formula → Substitution → Calculation → Final Answer.
• Use v² = u² + 2as when time is not given.
• Negative acceleration means retardation.
• If the body stops, final velocity (v) = 0.

CBSE & NEET Foundation Physics Notes

Practice Daily • Revise Formulas • Solve Numericals • Score Full Marks

Physics Special Units Guide: Length, Mass & Time | CBSE & NEET PrepPhysics Special Units Guide: Length, Mass & Time | CBSE & NEET Prep

Scaling the Universe: From the subatomic Fermi (10^{-15} \text{ m}) to the vastness of a Parsec (3 \times 10^{16} \text{ m}).

🔗 Internal Link 

 * "Basic SI Units and Dimensions": Link this when mentioning the "milli" or "kilo" prefixes to explain the base system.

 * "Errors in Measurement": Link to this after the "Scientific Notation" section to explain why precision matters.

 * "Atomic Structure": Link the Bohr Radius and amu values to your chemistry or atomic physics chapter.

 * "Work, Energy, and Power": Link the Horsepower (HP) and kWh conversions to the energy chapter.

Physics Quick Reference Guide

Special Units for Length

Fermi (f): 10^-15 m

Angstrom (Å): 10^-10 m

Nanometre (nm): 10^-9 m

Micron (μ): 10^-6 m

X-Ray Unit: ~10^-13 m

Bohr Radius: 0.5 × 10^-10 m

Mile: 1.609 km

Large Scale (Space):

• Astronomical Unit (AU): 1.496 × 10¹¹ m (Mean Sun-Earth distance)
• Light Year (ly): 9.46 × 10¹⁵ m (Distance light travels in 1 year at 3 × 10⁸ m/s)
• Parsec: 3.084 × 10¹⁶ m (3.26 light years)

Special Units for Mass & Time

Quintal: 100 kg

Metric Ton: 1000 kg

Atomic Mass Unit (amu): 1.67 × 10^-27 kg

Chandrasekhar Limit: 1.4 × Mass of Sun

Shake (Time): 10^-8 seconds

Prefixes for Powers of 10

Macro Prefixes (Multiples)
Multiplier	Symbol	Name
101	da	Deca
102	h	Hecto
103	k	Kilo
106	M	Mega
109	G	Giga
1012	T	Tera
1015	P	Peta

Micro Prefixes (Sub-multiples)
Multiplier	Symbol	Name
10-1	d	deci
10-2	c	centi
10-3	m	milli
10-6	μ	micro
10-9	n	nano
10-12	p	pico
10-15	f	femto

Important Conversions

1 km/h = 5/18 m/s	1 Newton = 105 dyne
1 Joule = 107 erg	1 Calorie = 4.18 Joule
1 eV = 1.6 × 10-19 J	1 HP = 746 W
1 Tesla = 104 Gauss	1 kWh = 3.6 × 106 J

Important Physical Constants

Constant	Value
Avogadro's Number (N)	6.023 × 1023 mol-1
Planck's Constant (h)	6.62 × 10-34 J·s
Permittivity of Free Space (ε₀)	8.854 × 10-12 F/m
Boltzmann's Constant (k)	1.38 × 10-23 J/K
Universal Gas Constant (R)	8.314 J·mol-1·K-1
Atmospheric Pressure (1 atm)	1.013 × 105 Pa

Units & Measurements: Practice Paper

I. Multiple Choice Questions (NEET Pattern)

NEET Q1. Which of the following is the largest unit of length?

A) Astronomical Unit B) Light Year C) Parsec D) Mile

Correct: C (Parsec). 1 Parsec = 3.26 light years ≈ 3.08 × 10¹⁶ m.

NEET Q2. The value of 1 Bohr radius is approximately:

A) 0.5 Å B) 1.0 nm C) 10^-15 m D) 1.6 km

Correct: A. Bohr radius is 0.5 × 10^-10 m, which equals 0.5 Angstrom (Å).

II. Short & Very Short Questions (CBSE Pattern)

1 Mark Q3. Define 'Shake'. What is its value in SI units?

Shake is a non-SI unit of time used in nuclear physics. 1 Shake = 10^-8 seconds.

2 Marks Q4. Differentiate between Astronomical Unit (AU) and Light Year (ly).

AU: Mean distance between Earth and Sun (1.496 × 10¹¹ m).
Light Year: Distance traveled by light in vacuum in one year (9.46 × 10¹⁵ m).

III. Assertion and Reason

Options: (A) Both A and R are true and R is correct explanation. (B) Both true but R is NOT correct explanation. (C) A is true, R is false. (D) A is false, R is true.

Assertion (A): Parsec is a unit used to measure time in astronomical observations.
Reason (R): 1 Parsec is equal to 3.26 light years.

Correct: D. Assertion is false because Parsec is a unit of distance, not time. Reason is true.

IV. Long Answer Questions (CBSE)

5 Marks Q5. List the macro and micro prefixes from 10¹⁵ to 10^-15. Explain why scientific notation is preferred over using full zeros in physics.

Students should list: Peta (10¹⁵), Tera, Giga, Mega, Kilo, Hecto, Deca... down to Femto (10^-15).
Reasoning: Scientific notation prevents "zero-counting" errors, makes multiplication/division easier (adding/subtracting exponents), and clearly indicates the precision (significant figures) of a measurement.

Dr.Sanjaykumar pawar

-Wed 25 Mar 2026

-4:02p.m