Niigata Public High School Entrance Examination - Science common mistakes
Niigata Public High School Entrance Examination - Science · Understand the traps and how to avoid them.
When asked to find the resultant force or the direction of motion, the candidate adds the magnitudes of two forces acting in different directions (for example, a horizontal pull and a downward weight) as if they were parallel, or subtracts them as if they were opposite, without drawing a force diagram first.
In junior-high mechanics, most practice problems involve forces along a single line, so the habit of combining magnitudes by simple addition or subtraction becomes automatic. When forces act at an angle (a cart pulled by a rope at a slant, an object on an incline, a ball at the top of a circular path), the candidate does not recognise that the forces must be resolved into components, and there is no explicit instruction in the question forcing them to draw the diagram.
What to do instead
Make a free-body sketch mandatory before any calculation: draw the object as a dot, draw each force as an arrow from the dot with a label, and mark the angle between each force and the chosen axis. For forces at an angle, resolve into horizontal and vertical components using the given angle and combine components separately. Practise a set of mixed problems (parallel, opposite, perpendicular, angled) and label each one as 'same line' or 'different lines' before solving.
The candidate treats 'speed is constant' and 'velocity is constant' as the same statement, and concludes that an object moving at constant speed in a circle or along a curved path has zero acceleration and zero net force.
Everyday language uses speed and velocity interchangeably, and most early motion graphs in class are straight lines where the distinction never matters. The curriculum introduces circular motion and changing direction qualitatively, so the candidate has no numerical routine that forces the distinction, and the term 'uniform motion' is misread as 'no force needed'.
What to do instead
Write the definition pair side by side in the notebook: speed = distance/time (a scalar), velocity = displacement/time (a vector with direction). For any curved-path problem, explicitly answer three questions in writing: (1) does the direction of motion change? (2) therefore is the velocity changing? (3) therefore is there a net force, and which way does it point? For circular motion, state that the net force points toward the centre.
On a distance–time or speed–time graph, the candidate reads the value off the vertical axis as the answer to 'how far did it travel' or 'what was its acceleration', instead of using the gradient of a distance–time graph for speed and the area under a speed–time graph for distance.
Graph questions reward quick reading of coordinates, and the candidate has practised 'read the graph' tasks in other subjects where the vertical value is the answer. The two different graph types look almost identical, and the candidate does not check which quantity is on each axis before choosing a method.
What to do instead
Before touching the graph, write the axis labels and units at the top of the working. Then apply a fixed rule: distance–time graph → gradient = speed, flat = at rest, straight = constant speed; speed–time graph → gradient = acceleration, area under line = distance travelled, flat above zero = constant speed. Work through one pair of graphs showing the same motion and compute both quantities from both, so the contrast is practised rather than read.
In a circuit with two resistors, the candidate applies the same current to both series resistors' voltage calculation and the same voltage to both parallel branches, without first deciding whether the components are in series or parallel and which quantity is shared.
The formulas V = IR, P = VI, and the series/parallel rules are memorised as separate facts, and under time pressure the candidate substitutes numbers into whichever formula comes to mind. The circuit diagram is treated as decoration rather than as the source of the constraint (current common in series, voltage common in parallel).
What to do instead
Adopt a two-line ritual for every circuit: line 1 writes 'series → I same, V splits' or 'parallel → V same, I splits'; line 2 writes the known values with units next to each component on the diagram. Then compute the total resistance first (series: add; parallel: use 1/R = 1/R1 + 1/R2), find the total current from the supply voltage, and only then work back to individual components. Check the answer by confirming the individual voltages add to the supply voltage in series, or the branch currents add to the total in parallel.
The candidate explains a magnetic effect or an induced current by saying 'the magnet attracts the coil' or 'the wire is magnetic', instead of describing the field direction and the resulting force direction using the right-hand or Fleming-type rule, and cannot state which way a compass needle or a current-carrying coil will turn.
Magnetism is taught largely through demonstrations, so the candidate remembers the phenomenon (the coil moves) but not the rule that predicts the direction. Direction rules are easy to confuse with each other, and the candidate avoids them by giving a vague causal story that sounds plausible.
What to do instead
Learn one direction rule thoroughly and practise it on paper: for a current-carrying wire in a field, use the left-hand rule (field, current, force mutually perpendicular) and for a coil, use the right-hand grip rule to find the field direction. For every problem, write the three directions as a labelled triple before answering. Then do five quick drills where only the direction is asked (no magnitudes), so the rule, not the phenomenon, is what gets rehearsed.
When a chemical equation is given, the candidate balances it by changing the subscripts inside a formula (writing H2O as H2O2, or Fe2O3 as FeO) rather than placing coefficients in front of the formulas, and then uses the altered formula in the mole calculation.
Balancing feels like an arithmetic puzzle, and adjusting a small number is faster than searching for a coefficient. The candidate has not internalised that a subscript defines the substance's identity, so changing it silently changes the chemistry and every subsequent mass or mole ratio.
What to do instead
Set a hard rule: only numbers written to the left of a formula may change. Balance in a fixed order (metals, then non-metals other than H and O, then H, then O), and after balancing, count each element on both sides and write the tally underneath. Add a final identity check: confirm every formula still matches the one given in the question and that the substances named in the stem are the ones in the equation.
The candidate calculates the mass of product from the mass of reactant without converting to amount of substance (moles), or converts one reactant but not the limiting one, and reports the answer as if the reactant present in the larger mass were always the limiting reactant.
Mass–mass problems look like proportional reasoning, so the candidate sets up a simple ratio of masses taken straight from the equation's coefficients, ignoring that coefficients count particles, not grams. The limiting-reactant idea is conceptually new and is often skipped when the numbers happen to look tidy.
What to do instead
Use a fixed four-step template for every stoichiometry problem: (1) write and balance the equation; (2) convert each given mass to moles using molar mass; (3) divide each mole amount by its coefficient and identify the smaller quotient as the limiting reactant; (4) convert the limiting reactant's moles to the wanted substance using the coefficient ratio, then back to mass. Write the units at every step, and finish by checking that the answer is less than the mass that would be obtained if the other reactant were limiting.
The candidate describes observations and conclusions as the same thing, writing 'the solution turned cloudy because a precipitate formed, so a chemical change occurred' as a single sentence, and cannot separate what was seen (colour change, gas bubbles, temperature rise, precipitate) from what was inferred (a new substance was produced).
Textbook explanations present observation and conclusion together, so the candidate memorises the combined sentence. Exam questions that ask specifically for 'what you observe' or 'what this shows' then receive a mixed answer that loses marks on the observation half or the reasoning half.
What to do instead
Train a two-column habit: left column 'observed' (only things visible or measurable: colour, bubbles, solid appearing, thermometer reading, mass change), right column 'inferred' (new substance formed, gas evolved, exothermic reaction). Practise by taking five familiar reactions and writing both columns for each. In the exam, underline the command word ('observe', 'explain', 'conclude') before writing and answer only that part.
When asked to explain a body process such as gas exchange, absorption, or filtration, the candidate names the organ or structure only ('oxygen goes to the lungs', 'the kidney filters blood') without linking structure to function, and omits the direction of movement or the mechanism (diffusion, concentration gradient, reabsorption, surface area).
Junior-high biology rewards naming, and many classroom questions stop at identification. The candidate therefore treats the structure name as a complete answer, and has not practised the causal chain from structure to function to the whole-body consequence.
What to do instead
For each organ system, memorise a three-link chain: structure → property that enables the function (thin walls, large surface area, dense capillaries, selective reabsorption) → direction and mechanism of movement. Write the chain out for alveoli, villi, and kidney tubules, then answer past-style questions using the full chain. Check each answer by asking whether it would still be true if the structure were removed, which exposes answers that are only names.
The candidate explains seasonal change, day and night, or the phases of the Moon by saying the Earth moves closer to and farther from the Sun, or that the Earth's distance from the Sun changes the seasons, and mixes up the Earth's rotation period with its revolution period.
The diagrams in textbooks are drawn not to scale, so the elliptical orbit looks strongly eccentric and distance seems a plausible cause. The two motions (spin and orbit) are taught close together, and the candidate has no mental model that keeps the 24-hour spin separate from the 365-day orbit and the 23.4° axial tilt.
What to do instead
Build one physical model and use it for every question: a tilted globe on a stick carried around a lamp, with the tilt direction fixed in space. Derive day/night from the spin, the year from the orbit, and the seasons from the tilt changing the angle and duration of sunlight, not the distance. Write the three quantities on a card (spin 24 h, orbit about 365 days, tilt 23.4°) and check every astronomy answer against the card before writing.