Question detail
A car engine has a total energy input of 200 kJ per kilometre and a useful energy output of 80 kJ per kilometre. Which statement best describes its efficiency?
Try the question, check the answer, then read the explanation to understand the curriculum point.
At a glance
MCQ
Type
practice
Style
Topic
Conservation and dissipation of energy
Question
- A. The engine is 80 % efficient.
- B. The engine is 40 % efficient.
- C. The engine is 200 % efficient.
- D. The engine is 120 % efficient.
Answer
The engine is 40 % efficient.
Explanation
The correct option is "The engine is 40 % efficient.". The engine is 40 % efficient. is right because it directly matches Efficiency: Recall and apply both efficiency equations.. The other options are less suitable because they change the required Physics relationship, confuse the relevant energy store or use a distractor that does not answer the question.
Common mistake
Confusing Efficiency Equations
Students often confuse the two efficiency equations, using useful energy output for total power input instead of total energy input.
Remember that efficiency can be calculated using either useful energy output divided by total energy input or useful power output divided by total power input. Always check which type of input is required.
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