Year 9 Science · Unit 3 · Lesson 11
Apply Worksheet
Learning Goals
1. Complete the table. For each quantity, write the equation used to calculate it and the unit of the answer.
| Quantity | Equation | Unit of the answer |
|---|---|---|
| Work done | ||
| Power | ||
| Gravitational potential energy | ||
| Energy to heat a substance |
2. Odd one out. Circle the item that does not belong in each group. Then explain why it does not fit.
| # | Group | Odd one out, and why |
|---|---|---|
| 1 | Conduction · Convection · Radiation · Inertia | |
| 2 | Expansion joint · Parachute · Bimetallic strip · Railway track gap | |
| 3 | Joule · Kilowatt-hour · Watt · Megajoule |
Real-world context: a chairlift at a ski resort
A chairlift in the Snowy Mountains carries skiers up a slope with a vertical rise of 300 m. On a busy morning it carries 1,200 skiers every hour. Take the mass of each skier, with gear, as 70 kg, and g as 10 N/kg.
Source: sample values for this worksheet.
3. Calculate (a) the work done lifting one skier to the top, (b) the work done lifting all the skiers in one hour, and (c) the useful power of the chairlift, in watts and kilowatts.
(a) One skier J
(b) One hour J
(c) Useful power W
(c) Useful power kW
4. The chairlift’s electric motor draws 100 kW. Calculate its efficiency, and explain what happens to the energy that does not lift the skiers.
Efficiency %
Investigation: a hand-crank torch
A student wound the handle of a hand-crank torch with a steady force of 15 N. On each turn, her hand moved 0.60 m in the direction of the force. A small meter measured the electrical energy the torch’s dynamo produced.
| Turns | Distance hand moved (m) | Work done by the hand (J) | Electrical energy out (J) | Efficiency (%) |
|---|---|---|---|---|
| 20 | 12 | 180 | 54 | 30 |
| 40 | 110 | |||
| 60 | 160 | |||
| 80 | 214 |
Source: sample class results.
5. Fill in the missing distances, work and efficiencies for 40, 60 and 80 turns. Give efficiencies as whole-number percentages.
6. Describe the pattern in the efficiency column. What happens to the energy that is not turned into electrical energy?
7. The 80 turns took 40 s. Calculate the student’s power input and the torch’s electrical power output. Explain why the output power is always smaller.
Power input W
Electrical power output W
Scenario: keeping a car engine cool
A petrol car engine turns about 25% of the chemical energy in its fuel into kinetic energy (the lesson’s value). A pump pushes coolant, which is mostly water, through channels in the hot metal engine and then through a thin metal radiator at the front of the car, where air rushes past. A plastic overflow bottle collects coolant when the engine is hot, and it flows back as the engine cools.
8. Explain how the cooling system stops the engine from overheating. Use at least four ideas from Lessons 1 to 10.