NCERT Class 9 Science — Chapter 1: Motion

mcqeasy

In the context of linear motion, acceleration is considered negative (retardation) when:

Official previous-year question

Verified 1 Aug 2026.

Options

AThe object is moving in a circular path.
BThe object starts from a state of rest.
CIt acts in the direction opposite to the velocity.
DIt acts in the same direction as velocity.

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Solution

Correct Option

The correct option is

It acts in the direction opposite to the velocity.

Explanation

Acceleration is a vector quantity defined as the rate of change of velocity with respect to time. In linear motion (motion along a straight line), the relationship between the direction of velocity and acceleration determines whether the speed of the object increases or decreases.

Detailed Analysis

It acts in the same direction as velocity. is incorrect: When acceleration acts in the same direction as velocity, the speed of the object increases. This is referred to as positive acceleration.
It acts in the direction opposite to the velocity. is correct: When acceleration acts in the direction opposite to the velocity, it opposes the motion. This causes the speed of the object to decrease over time. This phenomenon is technically termed negative acceleration, deceleration, or retardation.
The object is moving in a circular path. is incorrect: Motion in a circular path involves a continuous change in direction. While there is acceleration (centripetal), the term "retardation" specifically refers to a decrease in speed in linear contexts, not merely the geometry of the path.
The object starts from a state of rest. is incorrect: When an object starts from a state of rest, its velocity increases from zero. This requires a positive acceleration in the direction of motion to initiate movement.

Key Takeaway

Retardation (or negative acceleration) occurs strictly when the acceleration vector is directed opposite to the velocity vector, resulting in a reduction of speed.

Your note

More from Chapter 1: Motion

With reference to non-uniform acceleration, consider the following statements: 1. It occurs when velocity changes by unequal amounts in equal intervals of time. 2. A car increasing its speed by equal amounts in equal intervals of time is an example of non-uniform acceleration. 3. Free fall of a body is an example of non-uniform acceleration. Which of the statements given above is/are correct?

medium

Consider the following statements regarding the speed of sound and light: 1. Light travels faster than sound. 2. Thunder is heard before lightning is seen. 3. The speed of sound in air is approximately 346 km/s. Which of the statements given above is/are correct?

easy

In a hammer throw event, the hammer moves along a straight line tangential to the circular path upon release. This is because:

medium

With reference to the description of motion, consider the following statements: 1. The position of an object is described by specifying a reference point known as the origin. 2. An object's state of motion is absolute and independent of the observer. 3. Motion is inferred through the change in position of an object over time. Which of the statements given above are correct?

medium

Consider the following statements regarding 'distance' and 'displacement': 1. Distance is a vector quantity requiring both magnitude and direction. 2. Displacement is the shortest distance measured from the initial to the final position of an object. 3. The magnitude of displacement is equal to distance when motion is in a straight line. Which of the statements given above is/are correct?

easy

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Correct Option

The correct option is

It acts in the direction opposite to the velocity.

Explanation

Detailed Analysis

It acts in the same direction as velocity. is incorrect: When acceleration acts in the same direction as velocity, the speed of the object increases. This is referred to as positive acceleration.
It acts in the direction opposite to the velocity. is correct: When acceleration acts in the direction opposite to the velocity, it opposes the motion. This causes the speed of the object to decrease over time. This phenomenon is technically termed negative acceleration, deceleration, or retardation.
The object is moving in a circular path. is incorrect: Motion in a circular path involves a continuous change in direction. While there is acceleration (centripetal), the term "retardation" specifically refers to a decrease in speed in linear contexts, not merely the geometry of the path.
The object starts from a state of rest. is incorrect: When an object starts from a state of rest, its velocity increases from zero. This requires a positive acceleration in the direction of motion to initiate movement.

Key Takeaway

Retardation (or negative acceleration) occurs strictly when the acceleration vector is directed opposite to the velocity vector, resulting in a reduction of speed.