Year 9 Science · Unit 3 · Lesson 6

Energy Transfer and Work

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Learning Goals

Warm Up

Because… chain

Fill in the missing effects in the right-hand boxes. Each cause leads to the next effect. Follow the logic of work = force × distance.

Work = force × distance, so doing work requires both a force and a displacement.
→
Lifting a heavier object requires a greater upward force to overcome gravity.
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If the same distance is covered, a larger force means more joules of work done.
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More joules of work done means more energy has been transferred to the object.
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Overall outcome: What does this chain tell us about the relationship between the mass of an object and the energy needed to lift it?

Your Turn

Predict + reason

Scenario

Two construction cranes at a building site in Sydney are each lifting an identical 500 kg steel beam to the same height of 10 m. Crane A completes the lift in 30 seconds. Crane B completes the same lift but takes 5 minutes (300 seconds). Both cranes use a gravitational field strength of g = 10 N/kg.

(a) Calculate the work done by each crane. Are the values the same or different? Show your working. (Hint: W = F × d, and weight = mass × g)

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(b) Predict which crane has the higher power output, and calculate both power values using P = W ÷ t. Show your working.

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(c) A site manager says "Crane A is more powerful, so it does more work." Explain why this statement is incorrect, using your calculated values as evidence.

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Show What You Know

1. An electric motor does 24,000 J of work in 2 minutes. Calculate its power output in watts. Show your working and unit.

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2. Explain why a hiker walking a longer zig-zag trail up a mountain does the same work as one taking a direct steep path, but may feel more tired. Use the concepts of work, force, and distance in your answer.

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Wrap Up

In one sentence, what was the main idea of this lesson?

HSCScience · Year 9 Science · Unit 3 · Lesson 6 · Apply Worksheet