NYSTCE Physics common mistakes
NYSTCE Physics · Understand the traps and how to avoid them.
On inquiry and experimental-design items, the candidate selects the option stating that the data 'prove' the hypothesis, or reports an average of repeated trials without stating uncertainty, or fails to notice that a described setup lacks a control group or has a confounding variable (e.g., changing both the length and the mass of a pendulum).
Physics preparation emphasizes formula application, so experimental-reasoning items get skimmed. Candidates also carry over everyday language ('the experiment proves...') and treat repeated trials as automatically improving accuracy rather than only reducing random error.
What to do instead
Before answering, label the independent variable, dependent variable, and controlled variables in the prompt, and ask whether a systematic error (miscalibrated scale, zero error, parallax) would shift all readings in one direction. Phrase conclusions as 'supports' or 'is consistent with,' and report results as a mean plus a stated uncertainty or range. Averages of trials reduce random, not systematic, error.
In kinematics problems the candidate plugs numbers into v = v0 + at or y = v0t + ½at² without first fixing a coordinate axis, so a ball thrown upward is assigned a = +9.8 m/s² while upward is called positive, producing a negative time or a displacement with the wrong sign that is then reported as the answer.
Textbook equations are memorized as templates with g always '9.8,' and the sign is treated as part of the constant rather than as a consequence of a chosen axis. Under time pressure, drawing a diagram feels optional.
What to do instead
Write one line at the top of every solution: 'upward positive, origin at release point, a = −9.8 m/s².' Sketch the motion with velocity arrows at start, apex, and end. After computing, run two sanity checks: time must be positive, and at the apex v = 0 while a keeps the same sign throughout the flight.
The candidate applies conservation of mechanical energy (½mv² = mgh) to situations that include friction, air resistance, a applied braking force, or a perfectly inelastic collision, and then reports the speed as if all potential energy became kinetic energy.
Energy problems are visually similar whether or not they are conservative, and the qualifying phrases ('rough incline,' 'coefficient of friction 0.30,' 'the blocks stick together') are embedded in the stem rather than the question. The conservation equation is the first one recalled, so it is applied before the situation is classified.
What to do instead
Before writing any equation, list every force doing work on the object and mark each as conservative or non-conservative. If any force is non-conservative, use W_nc = ΔE (or ΔK = W_net) and compute the friction work as −f_k·d with f_k = μ_k·N. If the objects stick together, energy is not conserved; solve with momentum first, then compute the energy lost.
The candidate treats impulse and force as interchangeable, concluding that a longer collision time means a larger impulse, or that an airbag 'reduces the momentum change'; in two-dimensional collision items, momentum is added as a scalar (p1 + p2) rather than as perpendicular components.
Impulse J = FΔt contains both quantities, so the equation is misread as saying J grows with Δt regardless of the force. Momentum is introduced alongside energy, and the scalar habit from energy conservation carries over to a genuinely vector quantity.
What to do instead
Anchor on J = Δp = F_avg·Δt: for a fixed change in momentum, increasing the stopping time decreases the average force - that is the entire airbag argument. State explicitly that Δp is set by the before/after velocities, not by the collision duration. In 2-D problems, resolve into x and y components, conserve each axis separately, and remember that a large external impulse (friction over a long interval, gravity during a several-second event) invalidates momentum conservation for that system.
The candidate uses Q = mcΔT while a sample is melting or boiling, or states that an object 'has more heat' because its temperature is higher, and in calorimetry problems sets the heat gained by the cold body equal to the heat lost by the warm body without accounting for a phase change of the warm body.
The formula Q = mcΔT is drilled far more heavily than Q = mL, and 'heat' and 'temperature' are used interchangeably in everyday speech. During a phase change ΔT = 0, so the familiar equation produces zero and the phase term is silently dropped.
What to do instead
Build every calorimetry solution as a temperature timeline: sketch the warming curve and mark the plateaus. Apply Q = mcΔT only on sloped segments and Q = mL at each plateau, then sum. Treat heat as energy in transit, never as a substance an object 'contains'; internal energy and temperature are distinct, and two objects at the same temperature can require very different heat to warm further if their specific heats differ.
When using the thin-lens equation 1/f = 1/d_o + 1/d_i or the mirror equation, the candidate assigns signs inconsistently - entering a negative focal length for a converging lens, or reporting a positive image distance for a virtual image - and then mislabels the image as real and inverted.
Several sign conventions circulate (Cartesian, 'real-is-positive,' individual textbook variants), and mixed study sources leave the candidate with no single rule. The arithmetic produces a number that looks plausible, so the sign is never interrogated.
What to do instead
Commit to one convention and write it down before solving: for lenses, f is positive for converging and negative for diverging; d_i positive means a real image on the far side (inverted), d_i negative means a virtual image on the object side (upright, same side as object). Check the answer against a ray diagram - a single rough sketch of the three principal rays catches almost every sign error.
The candidate applies f_n = nv/2L to a pipe closed at one end, or forgets that a string fixed at both ends supports all integer harmonics while a closed pipe supports only odd harmonics; relatedly, the candidate uses the vacuum speed of light or sound speed unchanged when the wave enters a different medium or when a sound source moves.
The harmonic formulas look nearly identical, and the boundary condition (node versus antinode at each end) is treated as a detail rather than the source of the formula. Wave speed is memorized as a constant rather than as a property of the medium.
What to do instead
Derive rather than recall: draw the standing wave for the fundamental, count nodes and antinodes, and read off the wavelength (λ = 2L for a string or open pipe, λ = 4L for a closed pipe), then apply f = v/λ. Mark that a closed pipe gives odd n only. When a wave crosses into another medium, hold frequency fixed and recompute v and λ from the new medium's properties (v = √(T/μ) for a string, v = c/n for light).
The candidate treats electric potential as a vector and tries to add potentials directionally, or asserts that if E = 0 at a point then V = 0 there (or the converse), and concludes that a charge at the midpoint between two identical positive charges has no potential energy because the field cancels.
Field and potential are taught back-to-back, and the vector habits practiced with fields get transferred to a scalar quantity. The relation V = −∫E·dr is understood as a formula to manipulate rather than as a statement that only differences and gradients matter.
What to do instead
Fix the identities: potential is a scalar, so add algebraically with signs; field is a vector, so add by components. E = 0 does not imply V = 0 - at the midpoint of two like charges the field cancels but the potential is the (nonzero) sum of two positive terms, so a test charge there has maximum potential energy along that axis. Conversely, V can be zero where E is not, as at the midpoint of a dipole. Work from U = qV and E = −ΔV/Δx.
In circuit items the candidate says current is 'used up' as it passes through resistors so that the current is smaller after the first bulb, ignores internal resistance and reports the emf as the terminal voltage, or adds series and parallel resistors without redrawing the network to find which elements are actually in series versus parallel.
Series-circuit reasoning is often learned from water-flow analogies that imply consumption, and 'battery voltage' is used without distinguishing emf from terminal potential difference. Multi-resistor networks require redrawing, which candidates skip to save time.
What to do instead
State the invariants before computing: charge is conserved, so current is identical at every point in a series branch; in parallel branches the current splits but the voltage drop is the same. Use terminal voltage V_T = ε − Ir whenever internal resistance is given or implied. Redraw the circuit node by node, collapsing obvious series and parallel groups, and check the final equivalent resistance against the limiting cases (R_eq must exceed the largest series resistor and be smaller than the smallest parallel one).
The candidate claims that brighter (more intense) light produces photoelectrons with greater maximum kinetic energy, or that increasing intensity can eject electrons from a metal below its threshold frequency; in atomic items, the same candidate treats the photon energy as depending on intensity rather than on frequency.
Intensity feels like 'more energy,' so the classical wave picture is intuitively applied. The photoelectric result is counterintuitive and is usually memorized as a sentence ('intensity affects current, frequency affects energy') rather than as a consequence of E = hf and the work function.
What to do instead
Reason from K_max = hf − φ. Frequency alone sets the photon energy and therefore the maximum kinetic energy; below the threshold frequency, hf < φ and no emission occurs at any intensity. Intensity sets the number of photons per second, hence the saturation photocurrent, once emission is already happening. Rehearse the three graphs (K_max versus f, current versus V for different intensities) so the relationships become visual rather than verbal.