Covers NCERT Class 11 Physics Part I, Chapter "Laws of Motion". Section numbers below follow the standard chapter sequence — the chapter number itself can shift by ±1 between print editions, the internal section order does not.
Friction (static vs kinetic, angle of friction, minimum force to move a block), circular motion applications (banking of roads with/without friction, conical pendulum), pulley & connected-block systems (including pseudo force in accelerating lifts), Lami's theorem for concurrent-force equilibrium, and momentum-conservation collision problems.
Aristotle's fallacy: force is not needed to keep a body moving at constant velocity — Galileo/Newton's law of inertia corrects this. A body continues in its state of rest or uniform motion unless acted on by a net external force.
Newton's Second Law: F = dp/dt = ma (for constant mass). This is the working equation for nearly every numerical in this chapter — always define a consistent positive direction before writing it.
Third Law: action and reaction act on different bodies and are simultaneous — they never cancel each other for the same object. A very common assertion-reason trap confuses this with equilibrium of a single body.
Conservation of linear momentum follows directly from the third law for an isolated system: total momentum before = total momentum after, applied component-wise for 2D collisions.
Equilibrium of a particle under three concurrent, coplanar forces: Lami's theorem, F₁/sinα = F₂/sinβ = F₃/sinγ, where each angle is opposite to the corresponding force.
Static friction is self-adjusting up to a maximum f_s(max) = μₛN; once motion starts, kinetic friction f_k = μₖN applies and is very slightly less than the maximum static value (μₖ < μₛ generally).
Rolling friction is much smaller than sliding friction — this is why wheels are more efficient than dragging, and is a frequent one-line factual MCQ.
Circular motion needs a net centripetal (centre-seeking) force, F = mv²/r. Banking of roads reduces reliance on friction: for a frictionless banked curve, tanθ = v²/(rg); with friction, the safe speed range widens on both ends.
Conical pendulum: bob moves in a horizontal circle, string sweeps a cone; tanθ = v²/(rg) again — recognise this as structurally the same equilibrium as banking, just with tension replacing normal reaction.
Pseudo force (= −ma_frame) is added only in a non-inertial (accelerating) reference frame, e.g. inside a lift or accelerating truck — direction is always opposite to the frame's acceleration.
Original questions modelled on recurring NEET question types for this chapter — not verbatim reproductions of any official paper.
Scaled from direct NCERT application (Q1–Q6) to mixed NEET-level difficulty (Q7–Q15). Attempt in 18 minutes, then check the answer key.
For an ideal string (massless, inextensible) over a frictionless pulley, tension is identical on both sides — only changes if the pulley itself has mass/friction, or the string has mass. Say it as you set up every pulley problem.
Lift accelerating upward → apparent weight N = m(g+a) → feels heavier. Lift accelerating downward → N = m(g−a) → feels lighter. Free fall (a=g) → N = 0 → weightlessness.
Friction always opposes relative motion (or attempted motion) between the two surfaces in contact — never the motion of the body "in general." Always draw the relative-slip direction first, then friction points opposite to it.