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NEET 2023 Physics Question 7 Solution

Topic: System of Particles and Rotational Motion · Official NTA Booklet Code G5

Question

The angular acceleration of a body, moving along the circumference of a circle, is:

✓

Verified Against NTA Final Answer Key

Option (1) : along the axis of rotation

📚 System of Particles and Rotational Motion Easy

📋 Given Parameters & Problem Setup

Motion Body moving along the circumference of a circle

Target Vector Angular acceleration (α⃗)

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The 30-Second Exam Hall Shortcut: ⚡ The Axial Vector vs Polar Vector Golden Rule

⏱️ Save ~30 seconds

Angular velocity, angular momentum, and angular acceleration are AXIAL vectors — they ALWAYS point along the axis of rotation!

1 Distinguish polar vectors (force, linear velocity, linear acceleration lying in the plane of motion) from axial vectors.

2 Recall that θ⃗, ω⃗, α⃗, and L⃗ are defined by the right-hand grip rule perpendicular to the plane of rotation.

3 Hence, angular acceleration α⃗ MUST lie along the axis of rotation.

4 Centripetal acceleration is along the radius; tangential acceleration is along the tangent; but angular acceleration is along the axis of rotation.

5 Instant Option (1) in 3 seconds flat!

🛡️

Why You Can 100% Trust This Shortcut: Fundamental Rotational Kinematics · Vector Cross Product Definitions (Angular acceleration α⃗ = dω⃗/dt is strictly oriented along the rotational axis).

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Step-by-Step Rigorous Workflow & Mathematical Proof

Step 1

Definition of Angular Acceleration as an Axial Vector

Angular acceleration α⃗ is defined as the time rate of change of angular velocity ω⃗:

\vec{\alpha} = \frac{d\vec{\omega}}{dt}

Step 2

Directional Orientation via Right-Hand Rule

Angular velocity ω⃗ is an axial vector perpendicular to the orbital plane of rotation, pointing along the axis of rotation by the right-hand screw rule. Since α⃗ is the derivative of ω⃗ with respect to scalar time t, it must be parallel (if speeding up) or antiparallel (if slowing down) to ω⃗:

\vec{\alpha} \parallel \vec{\omega} \quad \implies \quad \vec{\alpha} \text{ is oriented along the axis of rotation}

Step 3

Contrast with Linear Acceleration Components

In circular motion, the linear acceleration consists of centripetal acceleration (radially inwards) and tangential acceleration (tangent to the circle), whereas angular acceleration governs rotational rate and is purely axial:

\vec{a}_{\text{linear}} = \vec{a}_c + \vec{a}_t = -\omega^2 \vec{r} + (\vec{\alpha} \times \vec{r})

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360° Option Elimination Engine Key Feature

Diagnose every choice: Know exactly why the right option works and why distractors fail.

4-Option Deep Scan

1 (1)

✓ 100% Correct

Verdict & Scientific Reason:

Angular acceleration is by definition an axial vector directed along the axis of rotation.

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Why this is airtight: None. Candidate understood the distinction between linear and rotational kinematic vectors.

2 (2)

✗ Incorrect

Verdict & Scientific Reason:

Describes centrifugal tendency in a rotating frame, not angular acceleration.

⚠️

Student Fallacy (Why candidates pick this trap): Candidate confused angular acceleration with fictitious centrifugal force.

3 (3)

✗ Incorrect

Verdict & Scientific Reason:

Describes centripetal (radial) acceleration a_c, which is a linear acceleration.

⚠️

Student Fallacy (Why candidates pick this trap): Candidate confused angular acceleration (α) with centripetal acceleration (a_c = v²/r).

4 (4)

✗ Incorrect

Verdict & Scientific Reason:

Describes tangential acceleration a_t = α r, which is linear, not angular.

⚠️

Student Fallacy (Why candidates pick this trap): Candidate confused angular acceleration (α) with tangential linear acceleration (a_t).

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NTA Trap Alert: Confusing Angular (α) with Tangential (a_t) or Centripetal (a_c) Acceleration

Many candidates see "acceleration" and "circle" and instantly jump to "towards the centre" (Option 3) or "along the tangent" (Option 4). They overlook the crucial word "ANGULAR".

🛡️ How to avoid the -1 mark: Read carefully: "Angular" acceleration = along axis of rotation. "Linear/Tangential" acceleration = along tangent. "Radial/Centripetal" = towards center.

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Core NEET Syllabus Standard

National Eligibility cum Entrance Test (NEET UG) · System of Particles and Rotational Motion Standard Benchmark

Core Scientific Principle Tested:

"Angular variables (θ, ω, α) are axial vectors directed along the axis of rotation per the right-hand screw rule."

Syllabus Focus: Kinematics of Rotational Motion and Axial Vectors

Preserved in Rationalized Curriculum Syllabus & Academic Standards ↗

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NEET 2023 Physics Question 7 Solution

Question

The 30-Second Exam Hall Shortcut: ⚡ The Axial Vector vs Polar Vector Golden Rule

Step-by-Step Rigorous Workflow & Mathematical Proof

Definition of Angular Acceleration as an Axial Vector

Directional Orientation via Right-Hand Rule

Contrast with Linear Acceleration Components

360° Option Elimination Engine Key Feature

NTA Trap Alert: Confusing Angular (α) with Tangential (a_t) or Centripetal (a_c) Acceleration

Core NEET Syllabus Standard

Ready to attempt under real exam pressure?

🔗 Related Questions — System of Particles and Rotational Motion

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