NCEA Level 1 AS92047 Flashcards for Energy Concepts
Use measurements, energy diagrams and supplied formulas to explain mechanical, thermal and electrical systems in NCEA Level 1 AS92047.
Mayelana naleli qoqo
A sled slows on rough ground even though its height stays the same. Where does its kinetic energy go? These 56 flashcards help you answer questions like that for NCEA Level 1 Physics, Earth and Space Science standard AS92047.
Start with system boundaries, observable changes and simple energy transfers. Then practise choosing an energy model from a scenario, working from supplied data to a result, reading graphs and energy diagrams, and explaining what changes when you vary one quantity. The deck moves from short observations and one-step calculations to explanations that connect evidence, an energy concept and a practical consequence.
The mechanical cards cover movement, lifting, work and friction. The thermal cards cover heating, cooling, phase changes and insulation. The electrical cards cover simple circuits, resistance, power and energy use. The assessment supplies the necessary formulas. The cards focus on applying them in context, so they skip stand-alone symbol drills and full mock papers.
Reviewed for the 2026 assessment against AS92047 version 3. The scenarios and explanations are original. The CC0 label applies to the original content and cover to the extent applicable rights exist.
This is an independent, unofficial study resource with no affiliation with or endorsement by NZQA. The deck contains original exercises and uses no copied exam questions, marking schedules or curriculum text. See the official NZQA requirements.
Amakhadi akuleli qoqo
Ikhadi 1
Umbuzo
A warm bowl of soup cools on a bench. If your system contains only the soup, where should you draw its boundary?
Impendulo
Around the soup. The bowl and room are outside that boundary, so energy transferred from the soup to either one leaves the system.
Ikhadi 2
Umbuzo
A seed pod falls and speeds up. Which energy changes can you infer for the seed pod and Earth together?
Impendulo
Gravitational potential energy decreases as height falls. The pod's kinetic energy increases as its speed rises.
Ikhadi 3
Umbuzo
A solid metal sample goes from 16 °C to 29 °C. What temperature change should you report as evidence?
Impendulo
Its temperature rose by 13 °C. Subtract 16 °C from 29 °C.
Ikhadi 4
Umbuzo
A battery powers a small reading lamp. What energy pathway would you show with arrows from the battery to the room?
Impendulo
Chemical energy in the battery → electrical energy transferred to the lamp → light and thermal energy transferred to the surroundings.
Ikhadi 5
Umbuzo
One machine transfers 60 J in 3 s and another transfers 60 J in 6 s. Which has greater average power?
Impendulo
The first machine. It transfers the same energy in half the time, so its average power is twice as large, 20 W compared with 10 W.
Ikhadi 6
Umbuzo
A hoist raises a 3 kg tool bag by 2 m. Use g = 10 N/kg. How much gravitational potential energy does the bag–Earth system gain?
Use ΔEₚ = mgΔh.
Impendulo
60 J. Multiply mass, gravitational field strength and vertical rise. That gives 3 × 10 × 2 = 60 J.
Ikhadi 7
Umbuzo
One end of a metal rod touches a hot surface. The other end warms up. What mechanism moves energy through the rod?
Impendulo
Conduction. Energy passes along the solid from its hotter end towards its cooler end.
Ikhadi 8
Umbuzo
A battery, switch and lamp are connected in one loop. What switch position would you mark on a circuit diagram to explain why the lamp goes out?
Impendulo
An open switch. The break in the loop stops current through the lamp.
Ikhadi 9
Umbuzo
A 2 kg glider slides at 3 m/s. What is its kinetic energy?
Use Eₖ = ½mv².
Impendulo
9 J. Half the mass times speed squared gives ½ × 2 × 3² = 9 J.
Ikhadi 10
Umbuzo
A solid block has mass 0.40 kg and specific heat capacity 500 J/(kg·°C). Its temperature rises by 12 °C. How much energy does it gain?
Use E = mcΔT.
Impendulo
2,400 J. Use E = mcΔT because the block stays solid. Multiply 0.40 × 500 × 12.
Ikhadi 11
Umbuzo
A motor lifts a bucket. You want to treat the motor's work as an energy input and the gravitational potential energy gain as a change within the system. What goes inside your boundary?
Impendulo
The bucket and Earth. Leave the motor outside so its work transfers energy across the boundary.
Ikhadi 12
Umbuzo
An ohmic resistor has 8 V across it and carries 0.5 A. What is its resistance?
Use V = IR.
Impendulo
16 Ω. Rearrange V = IR to get R = V ÷ I, then divide 8 V by 0.5 A.
Ikhadi 13
Umbuzo
A winch pulls a crate 5 m along a level floor with a steady 24 N force parallel to the motion. How much work does the winch do on the crate?
Use W = Fd.
Impendulo
120 J. Use W = Fd because the force points along the displacement. Multiply 24 N by 5 m.
Ikhadi 14
Umbuzo
A heater warms room-temperature water at the bottom of a tank. What motion should arrows show for the resulting convection current?
Impendulo
Warmed water rises and cooler water sinks to replace it. The warmed water is less dense than the cooler water around it.
Ikhadi 15
Umbuzo
A motor draws 0.30 A from a 12 V supply. How fast does it receive electrical energy?
Use P = VI.
Impendulo
3.6 W, or 3.6 J per second. Use P = VI and multiply 12 by 0.30.
Ikhadi 16
Umbuzo
A mixer receives 150 J from a battery. Its useful mixing action accounts for 90 J. How much goes to other outputs if its stored energy stays unchanged?
Impendulo
60 J. The other outputs account for the difference between the 150 J input and the 90 J useful output.
Ikhadi 17
Umbuzo
You have E = mcΔT and E = mL. Which applies to a pure solid melting at constant temperature?
Impendulo
E = mL. The energy goes into the change of state while the temperature stays at the melting point.
Ikhadi 18
Umbuzo
A climber follows a 7 m route up a wall and gains 4 m in height. Which distance belongs in the change in gravitational potential energy?
Impendulo
4 m. The change depends on the vertical rise above the starting point.
Ikhadi 19
Umbuzo
Where should you connect a voltmeter to measure the voltage across a lamp?
Impendulo
In parallel with the lamp. Connect one voltmeter terminal on each side of the lamp.
Ikhadi 20
Umbuzo
An infrared heater warms your hand across an evacuated gap. Which heat-transfer mechanism crosses the gap?
Impendulo
Radiation. Infrared waves can carry energy through a vacuum.
Ikhadi 21
Umbuzo
A stone drops from rest. Air resistance is negligible. An energy-bar diagram for the stone and Earth shows 30 J of gravitational potential energy at release. How should the total mechanical-energy bar change as the stone falls?
Impendulo
It should stay at 30 J. The loss of gravitational potential energy is matched by an equal gain in kinetic energy.
Ikhadi 22
Umbuzo
A fan draws a steady 9 W of electrical power for 2 min. How much electrical energy does it receive?
Use ΔE = Pt.
Impendulo
1,080 J. Convert 2 min to 120 s, then use ΔE = Pt = 9 × 120.
Ikhadi 23
Umbuzo
On a graph of cumulative energy transferred against time, line A has twice the slope of line B. What does that tell you about power?
Impendulo
A transfers energy at twice the rate of B. The slope gives energy per unit time, which is power.
Ikhadi 24
Umbuzo
Two blocks of equal mass each gain 800 J without changing state. Block A warms by 4 °C and B by 8 °C. Which has greater specific heat capacity?
Impendulo
Block A. With the same mass and energy gain, its smaller temperature rise means it takes more energy to warm each kilogram by 1 °C.
Ikhadi 25
Umbuzo
A loaded trolley travels at 2 m/s on one run and 6 m/s on another. Its mass stays the same. How should the two kinetic-energy bars compare?
Impendulo
The bar for 6 m/s should be nine times as tall. Tripling the speed multiplies kinetic energy by three squared when the mass is fixed.
Ikhadi 26
Umbuzo
A resistor's voltage–current graph has voltage on the vertical axis and current on the horizontal axis. What does the slope of the straight line through the origin give?
Impendulo
The resistance. The slope is voltage change divided by current change, equal to V ÷ I for this line through the origin.
Ikhadi 27
Umbuzo
A 0.15 kg frozen water sample at 0 °C melts completely. Use a latent heat of fusion of 334,000 J/kg. How much energy is absorbed during melting?
Choose from E = mcΔT and E = mL.
Impendulo
50,100 J. Use E = mL for the change of state. Multiply 0.15 kg by 334,000 J/kg.
Ikhadi 28
Umbuzo
A sled slows on level rough ground. Its height stays the same. How would you account for the drop in kinetic energy?
Impendulo
The sled and ground gain internal energy through friction. Some energy can also spread to the surroundings through sound.
Ikhadi 29
Umbuzo
A battery-driven hoist raises a planter at constant speed. Apart from sound and heating, which energy change belongs at the output end of the hoist's energy diagram?
Impendulo
An increase in the planter–Earth system's gravitational potential energy. The rising planter keeps the same kinetic energy because its speed is constant.
Ikhadi 30
Umbuzo
A lamp receives 80 J and emits 16 J as useful light. What fraction of the input is useful, expressed as a percentage?
Impendulo
20%. Divide the useful light energy by the electrical input, then multiply by 100.
Ikhadi 31
Umbuzo
A lid is fitted to a dish of warm water. Evaporation is negligible in both cases. How can the lid reduce cooling through the air above the water?
Impendulo
It reduces heat transfer by convection. Less warm air near the surface can move away and be replaced by cooler room air.
Ikhadi 32
Umbuzo
A cart moves 4 m while a 6 N friction force acts opposite its motion. How much energy does friction remove from the cart's mechanical energy?
Impendulo
24 J. Multiply force by distance to get the amount removed. Friction does −24 J of work on the cart because it points against the motion.
Ikhadi 33
Umbuzo
A resistor is swapped for one with twice the resistance. An ideal supply keeps the voltage across it fixed. How does the current change?
Impendulo
It halves. At fixed voltage, I = V ÷ R, so doubling the resistance halves the current.
Ikhadi 34
Umbuzo
A pure substance is heated at constant power and fixed pressure. On its temperature–time graph, a rising line becomes flat as the solid starts to melt. Why can the heater still transfer energy on that flat section?
Impendulo
The energy changes the state from solid to liquid. The temperature stays at the melting point while the solid and liquid coexist.
Ikhadi 35
Umbuzo
Two lifts each raise the same load through the same height. Lift A takes 5 s and lift B takes 15 s. How do their average useful powers compare?
Impendulo
Lift A provides three times the useful power. The lifts give the load the same gravitational potential energy gain, but A does it in one-third of the time.
Ikhadi 36
Umbuzo
An energy-flow diagram shows 100 J entering a pump, 65 J as useful output and 35 J heating the surroundings. What should the two output arrow widths show if widths represent energy?
Impendulo
The useful arrow should be wider. Use widths in the ratio 65:35 so the two outputs together have the input arrow's width.
Ikhadi 37
Umbuzo
At a fixed 6 V, a 12 Ω heating element is replaced by a 6 Ω element. Both are ohmic. How does electrical power change?
Impendulo
It doubles. The current rises from 0.5 A to 1 A, so P = VI rises from 3 W to 6 W.
Ikhadi 38
Umbuzo
A liquid sample of mass 0.20 kg receives 800 J. Its specific heat capacity is 2,000 J/(kg·°C). Assume no phase change or energy loss. How much does its temperature rise?
Choose from E = mcΔT and E = mL.
Impendulo
2 °C. Rearrange E = mcΔT to get ΔT = 800 ÷ (0.20 × 2,000).
Ikhadi 39
Umbuzo
Two ramps of different lengths bring the same crate to the same raised platform. The crate starts from the same floor each time. How do the gravitational potential energy gains compare?
Impendulo
They are equal. The mass, gravitational field strength and vertical rise are the same for both routes.
Ikhadi 40
Umbuzo
A pump receives 360 J from a supply while drawing a steady 12 W. How long was it running?
Impendulo
30 s. Divide the energy transferred by the power. That gives 360 J ÷ 12 W = 30 s.
Ikhadi 41
Umbuzo
A flask has an evacuated gap between its walls. Why might adding a shiny low-emissivity surface still reduce heat loss?
Impendulo
Radiation can cross the vacuum. The low-emissivity surface emits less infrared at the same temperature, reducing net radiative transfer across the gap.
Ikhadi 42
Umbuzo
A box sliding down a rough ramp loses 240 J of gravitational potential energy and gains 180 J of kinetic energy. Assume sound is negligible. What happened to the other 60 J?
Impendulo
It mainly increased the internal energy of the box and ramp. Mechanical energy fell by 60 J, and friction warmed the surfaces as they rubbed together.
Ikhadi 43
Umbuzo
Two ohmic heating wires are tested separately at the same current. Wire A has twice the resistance of wire B. Which receives more power?
Impendulo
Wire A receives twice as much power. At fixed current, twice the resistance needs twice the voltage, and P = VI doubles.
Ikhadi 44
Umbuzo
Pump A uses 200 J to give water 120 J of gravitational potential energy. Pump B uses 300 J to give water 150 J. Which uses its input more efficiently?
Impendulo
Pump A. It transfers 60% of its input to the water as useful energy. Pump B transfers 50%.
Ikhadi 45
Umbuzo
Two mugs hold equal masses of water at 80 °C. Assume negligible evaporation. After 5 min, one is at 68 °C and the other at 74 °C. What does this show about their average net energy loss per second?
Impendulo
The water that reached 68 °C lost energy at twice the average rate of the other sample. For equal masses and specific heat capacities, its 12 °C drop means twice the energy loss of the 6 °C drop over the same time.
Ikhadi 46
Umbuzo
A bead starts from rest and slides down a smooth wire. Air resistance is negligible. It has lost 6 J of gravitational potential energy at point A and 10 J at point B. What would you draw for its kinetic-energy bars?
Impendulo
A 6 J bar at A and a 10 J bar at B. Each bar equals the gravitational potential energy lost by that point.
Ikhadi 47
Umbuzo
Two lamps are connected to an ideal battery on separate parallel branches. One lamp's branch opens. Why can the other lamp stay on?
Impendulo
Its branch still makes a complete loop through the battery, so current can still flow through that lamp.
Ikhadi 48
Umbuzo
A 0.10 kg sample of ice at 0 °C melts, then the water warms. Use a latent heat of fusion of 334,000 J/kg, a liquid specific heat capacity of 4,200 J/(kg·°C) and a 10 °C rise. How much energy does the sample gain in total?
The available formulas are E = mcΔT and E = mL.
Impendulo
37,600 J. Melting takes 33,400 J from mL. Warming the resulting water takes another 4,200 J from mcΔT.
Ikhadi 49
Umbuzo
A winch pulls two identical crates one at a time with the same force along the direction of travel. Crate A moves twice as far as crate B. How does the work done by the winch compare?
Impendulo
The winch does twice as much work on A. With the same force parallel to the motion, W = Fd scales with distance.
Ikhadi 50
Umbuzo
At 2 V a component carries 0.20 A. At 4 V it carries 0.30 A. What evidence rules out one constant resistance over these readings?
Impendulo
The V ÷ I ratio changes. It is 10 Ω at the first reading and about 13.3 Ω at the second, so the data do not fit one straight line through the origin.
Ikhadi 51
Umbuzo
A bare metal tray and a foam-lined tray each hold an identical warm sample. Energy leaves mainly through the base. Why does the foam-lined tray keep its sample warm longer?
Impendulo
The foam slows conduction through the base. Less energy leaves per second, so the sample's temperature falls more slowly.
Ikhadi 52
Umbuzo
A 1 kg toy car and a 2 kg toy car have equal kinetic energies. How does the lighter car's speed compare?
Impendulo
The lighter car is about 1.41 times as fast. With half the mass, its speed squared must be twice as large to give the same kinetic energy.
Ikhadi 53
Umbuzo
An element takes 2 A at 9 V for 40 s. How much electrical energy enters the element?
The available formulas are ΔE = Pt and P = VI.
Impendulo
720 J. Find power from P = VI = 18 W, then multiply by 40 s.
Ikhadi 54
Umbuzo
Two solid blocks have the same specific heat capacity and absorb energy at the same constant rate with negligible losses. Block B has twice the mass of block A. How do the slopes of their temperature–time graphs compare?
Impendulo
Block B's slope is half as steep. Each block gains the same energy per second, so doubling the mass halves the temperature rise per second.
Ikhadi 55
Umbuzo
A crane adds 600 J of gravitational potential energy in 3 s. The motor receives 300 W of electrical power throughout. What fraction of the input power becomes useful lifting power?
Impendulo
Two-thirds, about 67%. The useful output is 600 J ÷ 3 s = 200 W, and 200 W ÷ 300 W gives the fraction.
Ikhadi 56
Umbuzo
A room heater sits near floor level. Warm air gathers near the ceiling. How can a small fan reduce the temperature difference between floor and ceiling?
Impendulo
It mixes the warm upper air with the cooler air below. Moving the air redistributes thermal energy around the room.
amakhadi angu-56
NCEA Level 1 AS92047 Flashcards for Energy Concepts
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