NCEA 91524: mechanical systems (Level 3 Physics)

What NCEA 91524 assesses

NZQA's standard limits the exam to a selection from four areas:

• Translational motion: centre of mass (1 and 2 dimensions), conservation of momentum and impulse (2 dimensions only).
• Circular motion and gravity: velocity, acceleration and resultant force for objects moving in a circle under two or more forces, Newton's law of gravitation and satellite motion.
• Rotating systems: constant angular acceleration, torque, rotational inertia, conservation of angular momentum and of energy.
• Oscillating systems: the conditions for simple harmonic motion, angular frequency, how displacement, velocity and acceleration vary with time, phasor diagrams and reference circles, damped and driven systems, resonance and energy.

Achieved shows awareness of how simple facets of phenomena relate to a situation. Merit gives explanations for the phenomena, concepts or principles. Excellence connects concepts or principles that relate to the situation.

The NCEA 91524 exam in 2026 and 2027

NCEA 91524 is one of three Level 3 Physics externals, with 91523 and 91526. The 2026 exam is on Thursday 12 November, in the afternoon session. NZQA's 2027 timetable is not out yet: it says exams run from 9 November to 3 December 2027. The 2026 and 2027 specifications match: you need an approved calculator, a ruler and a protractor, g is given as 9.81 m s⁻², and you may need to show mathematically that two principles are connected. Write down unrounded values in a "show that" question and give units.

How NCEA 91524 is marked: grade score marking

Each question scores N0 to E8 and the three add to 24. Substitution into p = mv or T = 2π√(m/k) banks a units, and explaining conservation or resonance in context supplies m and e.

NCEA 91524 cut scores

These are NZQA's cut scores for the total out of 24, taken from each year's assessment schedule. Over these five years Achieved needed 7 every time, Merit 13 or 14, and Excellence 19. The 2026 cut scores will appear in NZQA's 2026 schedule once the exam has been marked.

Worked examples at each grade

A trolley of mass 0.80 kg is tied to a spring of stiffness 320 N m⁻¹ and oscillates with amplitude 0.030 m.

Achieved: the period

Merit: maximum speed and acceleration, linked by energy

The angular frequency is ω = √(k ÷ m) = 20 rad s⁻¹. The maximum speed and acceleration occur at different places:

Merit explains why and checks it with energy: at the ends all the energy is stored in the spring, ½kA² = 0.144 J, and at the centre it is all kinetic, ½mv² = ½ × 0.80 × 0.60² = 0.144 J. The two match, so energy is conserved.

Excellence: angular momentum is conserved, energy is not

A turntable with rotational inertia 0.40 kg m² spins at 3.0 rad s⁻¹. A 2.0 kg lump of clay is dropped onto the rim, 0.50 m from the axis, and sticks. The clay adds I = mr² = 0.50 kg m². There is no external torque, so angular momentum is conserved:

The kinetic energy falls from ½ × 0.40 × 3.0² = 1.8 J to ½ × 0.90 × 1.33² = 0.80 J, a loss of 1.0 J. Excellence connects the two ideas: angular momentum is conserved because no external torque acts, but the clay sticking is an inelastic collision, so kinetic energy is transferred to thermal energy. Use "conserved" for quantities that stay the same in a system and "constant" only for a fixed value, a mix-up the 2025 NZQA report flags.

Try an impulse question in our Laws of Motion course, then press Mark to check your answer in the course:

Exam answers

The answers and a worked mark scheme come with today's paper once it is marked. We do not publish official or past paper answers. Every question on the daily paper is our own.

Use the daily paper as a practice exam

Uni-Sine publishes a free daily paper on the NCEA Level 3 Physics track, and a mechanics track, NCEA Level 3 Physics: Mechanics. They are short timed papers of 8 questions worth 25 to 35 marks, not full NCEA exams, and they are not written by NZQA. The Physics track includes circular motion, simple harmonic motion and gravitational fields and orbits, which sit inside 91524; the Mechanics track covers forces, moments and projectiles. Neither covers rotation or angular momentum, so rehearse those from your class notes. See the NCEA Level 3 Physics guide for the whole subject.

Common mistakes in NCEA 91524

NZQA's 2025 report on the Level 3 Physics exams says, for 91524:

• Vector directions. Candidates struggled with directions, and with formal equations of motion where they skipped algebraic steps.
• Constant versus conserved. "Constant" momentum was often used where "conserved" was meant.
• Simple harmonic motion and phasors. The report noted significant gaps.
• Terrestrial analogies in space. Applying roller coaster physics to space contexts stopped many reaching the top grade.
• Memorised model answers. The report says candidates lean too heavily on previous papers' model answers instead of applying knowledge to new situations.

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