Class 11 Physics Kinematics & Laws of Motion – Complete Guide

Class 11 Physics ka pehla real mechanics ka unit hai — Kinematics + Laws of Motion. 3 chapters (Motion in a Straight Line, Motion in a Plane, Laws of Motion) milke 16-marks portion banate hain. Yeh unit strong ho toh Work Energy Power, Rotational Motion, Gravitation, Oscillations sab easy ho jaate hain.

Marks Distribution

• Motion in a Straight Line — 4-5 marks
• Motion in a Plane — 6-7 marks (highest)
• Laws of Motion — 6 marks

Motion in a Straight Line

Kinematic Equations (Uniform Acceleration)

• v = u + at
• s = ut + ½at²
• v² = u² + 2as
• s_n = u + a(2n−1)/2

P-T graph slope = velocity; V-T graph slope = acceleration; V-T area = displacement.

Motion in a Plane (Vectors + 2D)

Vector = magnitude + direction. A = A_xî + A_yĵ + A_zk̂. Addition: parallelogram law R² = P² + Q² + 2PQ cosθ. Dot product A·B = AB cosθ (scalar); cross product A×B = AB sinθ n̂ (vector).

Projectile Motion — THE Star Topic

• Time of flight: T = 2u sinθ / g
• Max height: H = u² sin²θ / 2g
• Range: R = u² sin2θ / g (max at θ = 45°)

Board mein 5-mark question aksar; JEE Main mein 1-2 questions confirm.

Laws of Motion

Newton's three laws (inertia, F = ma, action-reaction). Momentum p = mv; Impulse J = Ft = Δp; conservation of momentum. Friction: f_s ≤ μ_sN, f_k = μ_kN, tanθ = μ. Circular motion: a = v²/r, F = mv²/r, banking tanθ = v²/rg.

Common Mistakes

• Sign convention nahi follow karna — direction pehle decide karo, consistent raho.
• Vectors ko scalars ki tarah treat karna — displacement ≠ distance.
• FBD skip karna — 'No FBD, no solution' rule.
• Friction direction galat — always opposite to (intended) motion.

Numerical Solving Method

1) Diagram banao, 2) given & required likho, 3) formula select karo (relation samjho), 4) substitute + units check.

Frequently Asked Questions