Q.20 Physics · Section A ⭐ 360° Option Elimination Active
NEET 2024 Physics Question 20 Solution
Topic: Motion in a Plane · Official NTA Booklet Code T1
Question
A particle moving with uniform speed in a circular path maintains:
✓
Verified Against NTA Final Answer Key
Option (2) : varying velocity and varying acceleration.
📚 Motion in a Plane Easy
📋 Given Parameters & Problem Setup
Motion Particle moving in a circular path
Speed Uniform speed (constant magnitude |v| = constant)
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⏱️ Save ~35 seconds The 30-Second Exam Hall Shortcut: ⚡ Vector Directionality Test
Speed is scalar (constant), but velocity and acceleration vectors continuously turn in space -> BOTH vary in direction!
1 Uniform circular motion has constant speed: |v| = v_0 = constant.
2 The velocity vector v is always tangential: as the particle moves around the circle, the direction of the tangent changes continuously -> Velocity is VARYING.
3 The centripetal acceleration vector a_c = (v²/R) points towards the center: its direction rotates continuously as the particle moves -> Acceleration is VARYING.
4 Therefore, both velocity and acceleration are varying vectors.
5 Option (2) in under 5 seconds!
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Why You Can 100% Trust This Shortcut: Fundamental Kinematics · Vector Definition of Velocity and Acceleration in Curved Paths.
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Step-by-Step Rigorous Workflow & Mathematical Proof
Step 1
Velocity Vector Analysis
Velocity is a vector quantity having both magnitude and direction. In uniform circular motion of radius R and angular velocity ω, the magnitude of velocity (speed) is constant, but its direction is along the instantaneous tangent to the circle:
Step 2
Evaluation of Velocity Constancy
Because the unit vector direction changes at every instant of time, the velocity vector is NOT constant:
Step 3
Acceleration Vector Analysis
Differentiating the velocity vector with respect to time yields the centripetal acceleration vector:
Step 4
Evaluation of Acceleration Constancy
While the magnitude of centripetal acceleration is constant (|a| = v²/R = ω²R), its direction always points radially towards the instantaneous position of the center, which rotates in space. Because its direction changes continuously:
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4-Option Deep Scan
360° Option Elimination Engine Key Feature
Diagnose every choice: Know exactly why the right option works and why distractors fail.
1 (1)
✗ Incorrect Verdict & Scientific Reason:
Velocity cannot be constant along a curved path.
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Student Fallacy (Why candidates pick this trap): Confusing constant speed with constant velocity.
2 (2)
✓ 100% Correct Verdict & Scientific Reason:
Both vectors continuously rotate, so both are varying.
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Why this is airtight: None.
3 (3)
✗ Incorrect Verdict & Scientific Reason:
Constant velocity implies zero acceleration and straight-line motion.
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Student Fallacy (Why candidates pick this trap): Ignoring directional change.
4 (4)
✗ Incorrect Verdict & Scientific Reason:
Constant acceleration vector implies parabolic projectile motion, not circular motion.
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Student Fallacy (Why candidates pick this trap): Confusing constant magnitude of centripetal acceleration with constant vector.
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NTA Trap Alert: Vector vs Magnitude (Scalar) Ambiguity
Aspirants often choose "constant acceleration" because its magnitude (v²/R) is constant.
🛡️ How to avoid the -1 mark: Acceleration without qualification ALWAYS means the full vector. A vector is constant ONLY IF both its magnitude AND direction are constant!
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Core NEET Syllabus Standard
Physics Core Kinematics · Motion in a Plane Standard Benchmark
Core Scientific Principle Tested:
"In uniform circular motion, speed and acceleration magnitude are constant, but the velocity and acceleration vectors are both continuously changing direction."
Syllabus Focus: Uniform Circular Motion
✓ Core NEET UG Syllabus Anchor Syllabus & Academic Standards ↗
Curved path turns the arrow around: Both V and A are varying bound!
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