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QLDPhysicsQuick questions
Unit 2: Linear motion and waves
Quick questions on Power and efficiency (QCE Physics Unit 2)
4short Q&A pairs drawn directly from our worked dot-point answer. For full context and worked exam questions, read the parent dot-point page.
What is treating $P = Fv$ as instantaneous when it is not?Show answer
$P = Fv$ gives instantaneous power for a constant force; it gives average power for an average force.
What is mixing up watts and joules?Show answer
Watts are power (J s$^{-1}$). Joules are energy. A $100$ W bulb running for $1$ s consumes $100$ J of electrical energy.
What is computing efficiency from forces, not energies?Show answer
Efficiency compares energy or power, not raw forces. The lifting force and pulling force in a pulley system can differ by a factor of two while still delivering the same work.
What is forgetting that efficiency is dimensionless?Show answer
Both numerator and denominator must use the same unit (joules with joules, watts with watts).
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