NCERT Class 9 Science — Chapter 1: Motion

mcqmedium

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

Official previous-year question

Verified 1 Aug 2026.

Options

AThe centripetal force continues to act after release.
BThe hammer possesses infinite inertia.
CThe acceleration becomes zero immediately after release.
DThe direction of motion at any instant is along the tangent to the circle.

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Solution

Correct Option

The correct option is

The direction of motion at any instant is along the tangent to the circle.

Explanation

This phenomenon is governed by Newton's First Law of Motion (Law of Inertia) and the vector nature of velocity in circular motion. In uniform circular motion, while the speed may remain constant, the direction of velocity changes continuously at every point.

Detailed Analysis

Direction of Velocity: In circular motion, the velocity vector of the body at any specific instant is always directed along the tangent to the circular path at that point.
Role of Centripetal Force: While the athlete spins the hammer, a centripetal force (tension in the chain) acts towards the center, constantly pulling the hammer inward and changing its direction to maintain the circular path.
Effect of Release: At the moment of release, the centripetal force ceases to act. According to the Law of Inertia, an object will continue to move in its current state of motion (direction and speed) unless acted upon by an external force.
Resulting Path: Since the direction of motion (velocity) at the exact instant of release is tangential to the circle, the hammer continues along that straight tangential line.

Option Analysis

The acceleration becomes zero immediately after release.: While acceleration (specifically centripetal acceleration) drops to zero upon release, this explains the straightness of the path, not specifically why it is tangential. The tangential direction is determined by the velocity vector.
The direction of motion at any instant is along the tangent to the circle.: This is Correct. The instantaneous direction of motion is defined by the velocity vector, which is always tangential to the circular path. Upon release, inertia maintains this specific direction.
The centripetal force continues to act after release.: This is Incorrect. The centripetal force is provided by the athlete holding the chain. Once released, this force vanishes.
The hammer possesses infinite inertia.: This is Incorrect. Inertia is a property of mass and is finite. Infinite inertia would imply that no force could ever change the object's state of motion.

Key Takeaway: In circular motion, the velocity vector is always tangential to the circle. When the centripetal force is removed, inertia causes the object to continue moving along that tangent in a straight line.

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

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

Under which condition is the displacement of a moving object zero, despite the distance travelled being non-zero?

easy

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Correct Option

The correct option is

The direction of motion at any instant is along the tangent to the circle.

Explanation

Detailed Analysis

Direction of Velocity: In circular motion, the velocity vector of the body at any specific instant is always directed along the tangent to the circular path at that point.
Role of Centripetal Force: While the athlete spins the hammer, a centripetal force (tension in the chain) acts towards the center, constantly pulling the hammer inward and changing its direction to maintain the circular path.
Effect of Release: At the moment of release, the centripetal force ceases to act. According to the Law of Inertia, an object will continue to move in its current state of motion (direction and speed) unless acted upon by an external force.
Resulting Path: Since the direction of motion (velocity) at the exact instant of release is tangential to the circle, the hammer continues along that straight tangential line.

Option Analysis

The acceleration becomes zero immediately after release.: While acceleration (specifically centripetal acceleration) drops to zero upon release, this explains the straightness of the path, not specifically why it is tangential. The tangential direction is determined by the velocity vector.
The direction of motion at any instant is along the tangent to the circle.: This is Correct. The instantaneous direction of motion is defined by the velocity vector, which is always tangential to the circular path. Upon release, inertia maintains this specific direction.
The centripetal force continues to act after release.: This is Incorrect. The centripetal force is provided by the athlete holding the chain. Once released, this force vanishes.
The hammer possesses infinite inertia.: This is Incorrect. Inertia is a property of mass and is finite. Infinite inertia would imply that no force could ever change the object's state of motion.