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How Things Work

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How Things Work

Harper, Hamish and Zach are checking the devices at a busy post office. Use energy transfers and forces to work out how each system works. Show your reasoning for written answers.

Energy pathways

Energy is transferred between stores and forms. In many devices, some energy is transferred to the surroundings, often as thermal energy or sound.

1.The post office uses a battery-powered hand torch during a power outage. Which pathway best describes the torch while it is switched on?

Chemical energy → electrical energy → light energy, with some thermal energy
Light energy → chemical energy → sound energy
Thermal energy → electrical energy → chemical energy

2.Harper switches on a small electric fan. Identify one useful output and one energy output that is not useful for cooling the room.

3.A sorting-belt motor receives 500 J of electrical energy. It transfers 350 J usefully to moving parcels. Calculate the efficiency as a percentage.

4.Zach says, “The sorting-belt motor wastes 150 J, so that energy disappears.” Is he correct? Explain what happens to the remaining energy.

5.Complete the energy pathway for the electric kettle in the staff area: electrical energy → energy transferred to the heating element.

6.Complete the energy pathway for the electric kettle in the staff area: energy is transferred to the water as energy.

Forces and moving systems

Forces can change an object's speed or direction. Gears alter how rotation is transferred, so a trade-off between turning force and speed may occur.

7.Hamish pushes a loaded mail trolley with a steady force across a level floor. The trolley moves at a constant speed. What can you infer about the resultant force on the trolley?

It is zero because the forces are balanced
It points forwards and makes the trolley accelerate
It points backwards and makes the trolley stop

8.A bicycle courier approaches a steep hill. Explain why selecting a low gear makes it easier to pedal uphill, and state the usual trade-off.

9.The post office wants its parcel belt to transfer more input energy into useful movement. Suggest one practical change and explain how it could reduce energy wasted to the surroundings.

10.A small rooftop solar panel receives light energy and supplies electricity to charge a handheld scanner. Name the energy input and useful output, then give one reason the system may not transfer all the input usefully.

11.Design a simple renewable-energy device that could help at a post office, such as lighting a sign or powering a small information display. State the renewable input, the useful output, one likely wasted output, and one feature that could improve efficiency.