Power: The Rate of Energy Transfer — Drills · Grade 8 Science
Chapter: Work & MachinesWhat these drills covers
By the end of Power: The Rate of Energy Transfer you should be able to:
- I can calculate energy-transfer rate in watts and distinguish power from energy.
- I can compare useful power and efficiency using the same defined output and interval.
4 questions, written answer, each with a worked explanation.
Vocabulary used: power, watt, average power, kilowatt, kilowatt-hour, model, evidence, system boundary, assumption.
Problem 1
Answer and explanation
No. It transfers the same stated 120 J over a longer interval, so its average power is smaller.
No. It transfers the same stated 120 J over a longer interval, so its average power is smaller.
Response criteria
- Use the supplied conditions and relevant evidence.
- Explain the scientific mechanism or calculation.
- State a meaningful limitation or testable next step.
Problem 2
Answer and explanation
The input energy or input power and the losses. Useful lifting power alone does not describe all energy entering the device.
The input energy or input power and the losses. Useful lifting power alone does not describe all energy entering the device.
Response criteria
- Use the supplied conditions and relevant evidence.
- Explain the scientific mechanism or calculation.
- State a meaningful limitation or testable next step.
Problem 3
Answer and explanation
No. Efficiency is a ratio. The power also depends on the energy amount and time interval.
No. Efficiency is a ratio. The power also depends on the energy amount and time interval.
Response criteria
- Use the supplied conditions and relevant evidence.
- Explain the scientific mechanism or calculation.
- State a meaningful limitation or testable next step.
Problem 4
Answer and explanation
The operating duration, actual average power, cycling and energy price are also needed. A rating describes a condition rather than every day’s use.
The operating duration, actual average power, cycling and energy price are also needed. A rating describes a condition rather than every day’s use.
Response criteria
- Use the supplied conditions and relevant evidence.
- Explain the scientific mechanism or calculation.
- State a meaningful limitation or testable next step.