Grade 8 · Science
Check an energy design against a target
Loading quiz…
Example & extra help
Try a sample
A model device receives 150 J and transfers 90 J as its intended useful output. The design target is at least 70% useful-output efficiency. Does this trial meet the target?
- No, it falls below the target.
- Input energy and useful output must be added to find efficiency.
- Yes, it meets the target.
- The efficiency is always 100%.
See the answer & why
No, it falls below the target.
Useful-output efficiency = × 100 = 60%. Compare this with 70%; no, it falls below the target.
A little hint: Divide the intended useful output by the energy input, then compare with the target.
Define which output is useful for the stated design; other transfers still belong in the energy accounting.
All questions