NEET Physics — Mechanics Complete Chapter Guide

Chapter Overview & Weightage

Mechanics is the largest and most important unit in NEET Physics. It covers kinematics, Newton’s laws, friction, work-energy theorem, rotational motion, and gravitation. With 8-10 questions per paper, this is where NEET Physics battles are won or lost.

Mechanics carries 20-25% weightage in NEET Physics — that’s 8-10 questions worth 32-40 marks. Newton’s laws, energy conservation, and projectile motion are tested every single year.

Year	NEET (Q count)	Key Topics Tested
2024	9	Projectile motion, work-energy theorem, friction on incline
2023	10	Newton’s 3rd law, rotational KE, gravitational PE
2022	8	Relative motion, moment of inertia, escape velocity

Key Concepts You Must Know

Tier 1 (Core — 60% of questions)

Kinematics: $v = u + at$ , $s = ut + \frac{1}{2}at^2$ , $v^2 = u^2 + 2as$
Projectile motion: horizontal range $R = \frac{u^2 \sin 2\theta}{g}$ , max height $H = \frac{u^2 \sin^2\theta}{2g}$ , time of flight $T = \frac{2u\sin\theta}{g}$
Newton’s laws: $F = ma$ , action-reaction pairs, free body diagrams
Friction: static ( $f_s \leq \mu_s N$ ), kinetic ( $f_k = \mu_k N$ )
Work-energy theorem: $W_{net} = \Delta KE$
Conservation of energy: $KE + PE = \text{constant}$ (when only conservative forces act)

Tier 2 (Frequently asked)

Circular motion: centripetal acceleration $a = v^2/r$ , banking of roads
Rotational motion: $\tau = I\alpha$ , rolling on incline, MOI of standard bodies
Gravitation: $F = GMm/r^2$ , orbital velocity $v_o = \sqrt{gR}$ , escape velocity $v_e = \sqrt{2gR}$
Centre of mass and collisions (elastic, inelastic)

Tier 3 (Occasionally asked)

Relative motion problems
Systems of particles
Variation of $g$ with height and depth

Important Formulas

v = u + at

s = ut + \frac{1}{2}at^2

v^2 = u^2 + 2as

s = \frac{u + v}{2} \cdot t

For free fall: $u = 0$ , $a = g = 9.8$ m/s $^2$ (downward)

Quantity	Formula
Horizontal range	$R = \frac{u^2 \sin 2\theta}{g}$
Maximum height	$H = \frac{u^2 \sin^2\theta}{2g}$
Time of flight	$T = \frac{2u\sin\theta}{g}$
Maximum range angle	$\theta = 45°$

Key insight: $R$ is same for $\theta$ and $(90° - \theta)$ , but $H$ is different.

F = \frac{GMm}{r^2}

g = \frac{GM}{R^2}

v_{\text{orbital}} = \sqrt{\frac{GM}{R}} = \sqrt{gR}

v_{\text{escape}} = \sqrt{\frac{2GM}{R}} = \sqrt{2gR} = \sqrt{2} \cdot v_{\text{orbital}}

Variation of g: At height $h$ : $g' = g\left(1 - \frac{2h}{R}\right)$ (for $h \ll R$ )

At depth $d$ : $g' = g\left(1 - \frac{d}{R}\right)$

For NEET, projectile motion questions almost always involve either maximum range ( $\theta = 45°$ ) or finding the angle that gives equal range ( $\theta$ and $90° - \theta$ ). Master these two scenarios and you handle 80% of projectile problems.

Solved Previous Year Questions

PYQ 1 — NEET 2024

Problem: A body is projected with velocity 20 m/s at angle 30 degrees with horizontal. Find the maximum height reached. ( $g = 10$ m/s $^2$ )

Solution:

H = \frac{u^2 \sin^2\theta}{2g} = \frac{20^2 \times \sin^2 30°}{2 \times 10} = \frac{400 \times 0.25}{20} = \mathbf{5 \text{ m}}

PYQ 2 — NEET 2023

Problem: A block of mass 2 kg slides down a rough incline of angle 30 degrees with constant velocity. Find the coefficient of kinetic friction.

Solution:

Constant velocity means net force = 0 (acceleration = 0).

Forces along the incline: $mg\sin\theta = \mu_k mg\cos\theta$

\mu_k = \tan\theta = \tan 30° = \frac{1}{\sqrt{3}} \approx \mathbf{0.577}

When a body slides with constant velocity on an incline, $\mu_k = \tan\theta$ . This is one of the cleanest results in mechanics — no need to know the mass. NEET uses this repeatedly.

PYQ 3 — NEET 2022

Problem: The

escape velocity from Earth’s surface is $v_e$ . What is the escape velocity from a planet with twice the mass and twice the radius of Earth?

Solution:

v_e = \sqrt{\frac{2GM}{R}}

For the new planet: $M' = 2M$ , $R' = 2R$

v_e' = \sqrt{\frac{2G(2M)}{2R}} = \sqrt{\frac{2GM}{R}} = v_e

Answer: The escape velocity remains $\mathbf{v_e}$ (unchanged).

Difficulty Distribution

Difficulty	% of Questions	What to Expect
Easy	35%	Direct formula application (projectile, free fall, basic Newton’s law)
Medium	45%	Incline + friction, energy conservation with multiple forces, gravitation
Hard	20%	Rotational + translational combined, multi-step energy problems

Expert Strategy

Weeks 1-2: Kinematics and Newton’s laws — the foundation. Drill free body diagrams until you can draw them instantly. Every mechanics problem starts with a good FBD.

Weeks 3-4: Energy methods and rotational motion. Work-energy theorem is the fastest way to solve many mechanics problems. For rotation, memorise MOI values and the rolling condition ( $v = R\omega$ ).

Week 5: Gravitation and revision. Gravitation is formulaic — memorise the key equations and practice numerical substitution. Revise using PYQs sorted by topic.

NEET mechanics problems are rarely theoretical — they’re numerical. The typical format is: given a scenario, calculate a quantity. Speed of formula recall directly translates to marks. Make a formula sheet and revise it daily in the last month before NEET.

Common Traps

Trap 1 — Using $g = 9.8$ when the problem says $g = 10$ . NEET often simplifies $g = 10$ m/s $^2$ for easier calculation. Using 9.8 gives wrong numerical answers and wastes time.

Trap 2 — Forgetting that friction is kinetic during motion, static before motion starts. A block at rest on an incline uses $\mu_s$ (static). Once sliding, switch to $\mu_k$ (kinetic). Also, static friction adjusts up to $\mu_s N$ — it’s not always at its maximum value.

Trap 3 — Range is maximum at 45 degrees, NOT maximum height. Maximum height increases with angle up to 90 degrees. Maximum range is at 45 degrees. NEET places these as options together.

Trap 4 — Escape velocity doesn’t depend on the mass of the escaping object. $v_e = \sqrt{2GM/R}$ has no $m$ (mass of object) in it. A bullet and a spacecraft need the same escape velocity from the same planet. Students often think heavier objects need higher escape velocity.

Trap 5 — $g$ decreases both with height and depth, but by different formulas. With height: $g' = g(1 - 2h/R)$ . With depth: $g' = g(1 - d/R)$ . At the centre of Earth ( $d = R$ ), $g = 0$ . These formulas are different — don’t mix them up.