SRMHCAT cheat sheet

Equations of motion: v = u + at, s = ut + ½at², v² = u² + 2as apply only for constant acceleration; average velocity = (u+v)/2.

Newton's second law: net force F = ma; friction f = μN, and on an incline the driving component is mg sinθ while N = mg cosθ.

Work-energy theorem: W_net = ΔKE; gravitational PE = mgh, spring PE = ½kx², and mechanical energy is conserved when only conservative forces act.

Momentum is conserved in all collisions; in perfectly elastic collisions KE is also conserved, while perfectly inelastic collisions merge bodies with common velocity.

Circular motion: centripetal acceleration a = v²/r = ω²r; banking angle satisfies tanθ = v²/(rg) for frictionless turns.

Ohm's law V = IR; series resistance adds (R = R₁ + R₂), parallel gives 1/R = 1/R₁ + 1/R₂; power P = VI = I²R = V²/R.

Lens/mirror formula 1/f = 1/v − 1/u (signs per convention); power of a lens in dioptres P = 1/f with f in metres.

Photoelectric effect: maximum kinetic energy = hν − φ, where φ is the work function; emission occurs only above threshold frequency ν₀ = φ/h.

Mole concept: 1 mole = 6.022×10²³ particles = molar mass in grams; at STP one mole of ideal gas occupies 22.4 L.

Ideal gas law PV = nRT with R = 0.0821 L·atm/(mol·K) or 8.314 J/(mol·K); temperature must be in kelvin.

Molarity M = moles solute / litres solution; dilution obeys M₁V₁ = M₂V₂.

pH = −log[H⁺]; pH + pOH = 14 at 25 °C; strong acid/base fully dissociates, weak ones need Ka or Kb.

Le Chatelier's principle: adding reactant or removing product shifts equilibrium forward; increasing pressure favours the side with fewer gas moles.

Oxidation is loss of electrons (increase in oxidation number), reduction is gain; in a cell oxidation occurs at the anode.

Hybridisation from steric number: 2 → sp (linear), 3 → sp² (trigonal planar), 4 → sp³ (tetrahedral), 5 → sp³d, 6 → sp³d².

Bond order from molecular orbital theory = (bonding − antibonding electrons)/2; higher bond order means shorter, stronger bond.

Central dogma: DNA → RNA (transcription) → protein (translation); codons are triplet and the code is degenerate but unambiguous.

Mitosis yields two diploid daughter cells; meiosis has two divisions and produces four haploid cells with crossing over in prophase I.

Photosynthesis: light reactions in thylakoids split water and yield ATP and NADPH; the Calvin cycle in the stroma fixes CO₂ via RuBisCO.

Cellular respiration: glycolysis in cytoplasm (net 2 ATP), Krebs cycle in mitochondrial matrix, oxidative phosphorylation on the inner membrane.

Mendelian ratios: monohybrid F₂ phenotype 3:1, dihybrid F₂ 9:3:3:1; test cross with recessive reveals genotype.

Human blood groups: AB has both antigens (universal recipient), O has none (universal donor); Rh factor matters in pregnancy.

Nephron function: filtration in the glomerulus, selective reabsorption mainly in the proximal tubule, and concentration via the loop of Henle.

Enzymes lower activation energy, are not consumed, and show specificity; rate rises with temperature up to an optimum then denatures.

Percentage change: successive changes of a% and b% give net change a + b + ab/100 percent, not a + b.

Simple interest = PRT/100; compound interest amount A = P(1 + R/100)^T for annual compounding.

Speed–time–distance: distance = speed × time; for equal distances at speeds x and y, average speed = 2xy/(x + y).

Work: if A alone takes a days and B alone b days, together they take ab/(a + b) days.

Permutations nPr = n!/(n − r)!; combinations nCr = n!/(r!(n − r)!), and nCr = nC(n − r).

Ratio and mixtures: alligation gives ratio of two quantities from their weighted mean; repeated dilution leaves original × (1 − k/V)^n.

Series patterns: check differences, ratios, squares/cubes, and alternating sub-series before assuming a single rule.

Syllogism rule: a conclusion follows only if true in every possible Venn arrangement of the premises; 'some' statements do not convert to 'all'.

Time allocation heuristic: in a 4-section paper of equal marks, budget roughly proportional to marks per question, and attempt one-mark factual items before multi-step numericals.

Unit check as a filter: if a computed answer's units do not match the quantity asked (for example J instead of N), the step is wrong.

Approximation rule: for numerical MCQs, round constants (g ≈ 10 m/s², π ≈ 3) only when answer options are far apart.

Negative marking: attempt a guess only if at least two options can be eliminated, since a 1/3 chance beats a −1/4 penalty only above 25% confidence.

Diagram-first method for reasoning: redraw seating, blood-relation, or direction puzzles as a labelled sketch before evaluating options.

Dimension and scale sanity check: a human-scale answer (speed, mass, current) far outside plausible ranges signals an arithmetic slip.

Data interpretation: compute percentage change from the base value, and read axis scales before comparing bar or line heights.