Maharashtra SSC Science and Technology (MSBSHSE) common mistakes
Maharashtra SSC Science and Technology (MSBSHSE) · Understand the traps and how to avoid them.
Writes F = G m1 m2 / r^2 and substitutes r = 6.4 x 10^3 (the value in km) and masses in grams, then labels the answer 'N' without any conversion step.
Textbook gravitation problems quote Earth's radius in km and pull masses in grams, and the formula looks unit-free, so units get treated as labels to attach at the end rather than quantities carried through the calculation.
What to do instead
Force a conversion line before substitution: r = 6.4 x 10^3 km = 6.4 x 10^6 m, m = 100 g = 0.1 kg. Then confirm with the unit of G (N m^2 kg^-2) that the result must come out in newton; if the unit check fails, the substitution was wrong.
For a bus decelerating at 2 m/s^2, substitutes a = +2 m/s^2 into v = u + at and reports a final velocity larger than the initial velocity.
The question supplies a magnitude ('deceleration 2 m/s^2') and students copy the number straight into the equation without first assigning a positive direction to the motion.
What to do instead
Before touching any equation, draw an arrow along the motion and write 'forward = +'. Deceleration then becomes a = -2 m/s^2. Use the physical check that for a stopping body v must be less than u, and reverse the sign if it is not.
Calculates the heat needed to melt 10 g of ice at 0 degrees C using Q = mc x delta-T with delta-T = 0 and concludes that no heat is required.
Every earlier calorimetry numerical used Q = mc x delta-T, so the flat plateau of the heating curve, where temperature stays constant during the phase change, has no number to plug in and gets skipped.
What to do instead
Split the problem into named stages: Q = m x L(fusion) = 10 x 80 cal while melting, and Q = m x c x delta-T only where the temperature actually changes. Sketch the temperature-versus-heat curve and mark which formula applies to each segment.
In 1/v - 1/u = 1/f, substitutes f = +10 cm for a concave lens because 'focal length is a length', then reports a real image.
The sign convention is a bookkeeping rule rather than a physical length, and students assume distances are always positive, forgetting that a concave lens diverges rays and cannot form a real image of a real object.
What to do instead
Write a sign table at the top of the answer: distances measured against the incident light are negative, so u is negative and f is negative for a concave lens. Cross-check the conclusion: concave lens must give negative v, virtual, erect and diminished image.
Calculates the equivalent resistance of 6 ohm and 3 ohm in parallel as 9 ohm by adding them, then divides the total current using that value.
The series rule is learned first and is arithmetically easier, while the parallel form 1/Rp = 1/R1 + 1/R2 requires an extra reciprocal step where the inversion is often forgotten or applied to the wrong side.
What to do instead
Use Rp = (R1 x R2)/(R1 + R2) = 18/9 = 2 ohm and always check that Rp is smaller than the smallest branch resistance. That single sanity test catches nearly every add-instead-of-invert error before the current is calculated.
Balances Fe + H2O -> Fe3O4 + H2 by rewriting water as H3O or Fe3O4 as FeO, that is, by changing subscripts inside the formulas instead of placing coefficients in front.
Subscripts and coefficients both sit next to element symbols and both appear to 'fix' an atom count, so altering the formula feels like a legitimate and faster balancing move.
What to do instead
Apply the rule that subscripts identify the substance and can never be touched; only whole-number coefficients go in front. Balance atom by atom in a small table (Fe, H, O) and recount; if a formula seems to need changing, the product chosen is wrong.
States that a solution of pH 5 is more acidic than pH 2 because 5 is greater than 2, and calls a pH 12 solution a strong acid.
pH is read as an ordinary concentration-like number, whereas it is an index that runs opposite to hydrogen-ion concentration and changes by factors of ten, not by units.
What to do instead
Use pH = -log10[H+]: each unit down means ten times more H+ ions. Anchor three points in memory, pH 2 is strongly acidic, pH 7 neutral at 25 degrees C, pH 12 strongly basic, and convert any new value relative to those anchors before answering.
Names CH3CH2COOH as 'propanoic acid' by counting only the alkyl carbons, and names CH3CHO as 'methanal' by treating the carbonyl carbon as part of the group rather than the chain.
The functional-group carbon is mentally filed with the group (-COOH, -CHO) instead of being counted as a chain member, so the whole carbon skeleton is under-counted by one.
What to do instead
Count total carbons first, then number the chain so the -COOH or -CHO carbon is C-1: CH3CH2COOH is butanoic acid, CH3CHO is ethanal, HCHO is methanal. Write the condensed formula with every carbon visible before naming.
Predicts that a plant cell placed in hypotonic water will burst 'just like a red blood cell' because the plasma membrane is semipermeable.
Osmosis across the plasma membrane is learned first and vividly, so the cellulose cell wall is treated as a passive covering rather than a rigid structure that resists expansion and builds turgor pressure.
What to do instead
State the wall explicitly in the answer: in a hypotonic solution the plant cell becomes turgid, the wall limits swelling, and lysis does not occur. Only wall-less animal cells burst. Contrast the two outcomes side by side as a two-line comparison.
Writes the F2 phenotypic ratio of a Mendelian dihybrid cross as 3:1, or labels the 9:3:3:1 ratio as the genotypic ratio.
The monohybrid 3:1 result is over-learned and gets reused automatically, and the nine distinct genotypes hidden inside the 9:3:3:1 phenotype classes are never separated by counting.
What to do instead
Build the 4x4 Punnett square and count phenotypes (round-yellow, round-green, wrinkled-yellow, wrinkled-green) to get 9:3:3:1; count genotypes separately as nine classes in the ratio 1:2:1:2:4:2:1:2:1. Underline which ratio the question actually asks for before writing it.