NY Regents Physics common mistakes
NY Regents Physics · Understand the traps and how to avoid them.
Reporting a vector quantity (velocity, acceleration, force, momentum, displacement) as a bare number with no direction, or giving direction as a vague word like 'backward' without a reference axis.
Students memorize magnitude formulas and treat the sign or angle as decoration; the Reference Tables give magnitude equations, so the direction step feels optional and gets dropped under time pressure.
What to do instead
For every vector answer, force yourself to write two lines: magnitude with units, then direction stated relative to a named axis (e.g., '12 m/s at 30° north of east' or '5 N to the left'). Before solving, draw the axis and label which way is positive.
Using g = 9.81 m/s² and mixing it with values given to two significant figures, or switching between 9.8 and 10 mid-problem, producing answers that disagree with the accepted range.
Students pull g from the Reference Tables (9.81) but the problem's data imply 9.8; inconsistent rounding cascades through multi-step kinematics and projectile work.
What to do instead
Pick one value of g at the start of each problem (use 9.8 m/s² unless told otherwise), write it down, and carry extra digits through intermediate steps, rounding only the final answer to the significant figures of the given data.
Treating the top of a projectile's path as a point where velocity is zero, or assuming horizontal and vertical motions share the same time only 'sometimes'.
Everyday intuition says a ball 'stops' at its peak; students conflate vertical velocity (zero at apex) with total velocity (equal to the constant horizontal component there).
What to do instead
Split every projectile into independent x (constant velocity) and y (constant acceleration) columns. State explicitly: at the apex v_y = 0 but v_x is unchanged; the single flight time t links both columns. Practice labeling v_x and v_y at launch, apex, and landing.
Setting up Newton's second law on the wrong object or omitting a force from the free-body diagram, especially normal force, friction direction, or the force one surface exerts on another in a two-body problem.
Students draw the diagram from memory of similar problems rather than from the physical situation, and they forget that friction opposes relative motion, not necessarily the applied force.
What to do instead
Always draw the free-body diagram first with one object isolated, name each force and its source, then write ΣF = ma along chosen axes. For connected bodies, draw a separate diagram for each mass and use the same magnitude of tension/contact force.
Confusing conservation of mechanical energy with conservation of momentum, or applying energy conservation when friction is present without accounting for the energy dissipated.
Both are 'conservation' laws with similar-looking equations, and students default to whichever they saw last; they also forget that mechanical energy is only conserved in the absence of non-conservative work.
What to do instead
Before choosing a law, ask: is the system isolated (momentum) and are there non-conservative forces (energy)? Write the full work-energy statement ΔKE + ΔPE = W_nonconservative and only set the right side to zero when friction and applied forces are absent.
Mixing up series and parallel rules for current, voltage, and equivalent resistance, e.g., adding resistances in parallel directly or claiming current is the same through parallel branches.
The reciprocal formula for parallel resistance looks unlike the series sum, and students memorize 'current is constant' from series circuits and overgeneralize it.
What to do instead
Anchor on physics, not formulas: in series there is one path so current is common and voltages add; in parallel there are multiple paths so voltage is common and currents add. For parallel, compute 1/R_eq = Σ1/R_i and sanity-check that R_eq is smaller than the smallest branch.
Reversing the direction of induced current or magnetic force by mishandling a right-hand rule, or forgetting that the force on a moving charge is perpendicular to both velocity and field.
Multiple right-hand rules (force on charge, field around a wire, induced current) get blended, and students apply them to the wrong finger or hand.
What to do instead
Write the rule you are using next to the diagram every time (e.g., 'F = qv×B: fingers along v, curl to B, thumb gives F for positive charge; reverse for negative'). Do a quick 90° check: the force must be perpendicular to the velocity.
Treating wave speed, frequency, and wavelength as if changing one medium property changes all three, or believing frequency changes when a wave enters a new medium.
The equation v = fλ has three variables, and students assume any change propagates to all of them; they forget frequency is set by the source.
What to do instead
State the invariant first: frequency is fixed by the source and does not change across a boundary; speed is set by the medium, so wavelength adjusts (λ = v/f). Use this to predict refraction direction and to check answers.
Misreading ray diagrams or applying the mirror/lens equation with wrong sign conventions, then reporting a virtual image as real (or vice versa).
Sign conventions differ between mirror and lens setups and are rarely drilled; students plug numbers without tracking whether image distance is positive or negative.
What to do instead
Write the sign convention at the top of the problem (for a single converging lens: f positive, real object distance positive, negative image distance means virtual upright image). Confirm with a quick sketch: virtual images form on the same side as the object for lenses and are always upright.
Mishandling photon-energy and photoelectric problems by using wavelength in nanometers directly in E = hc/λ, or ignoring the work function threshold when deciding whether emission occurs.
Unit conversion (nm to m) is skipped under time pressure, and students compute photon energy but never compare it to the work function to check if electrons are actually ejected.
What to do instead
Convert wavelength to meters before substituting, and always write the photoelectric condition: emission occurs only if hf ≥ φ; the maximum kinetic energy is K = hf − φ. State both the threshold check and the K value in the answer.