Measuring mechanical power via work and time

Steps:

• Power output is calculated as P = W/t, where W is work done (force × distance) and t is time.
• Force comes from the known load's weight (mass × g).
• Distance is the vertical height lifted, measured directly.
• Time is the duration to lift the load, measured precisely.

Why C is correct:

• Metre rule measures height (distance) for work (W = F × d); stop-watch measures time (t) for power (P = W/t), per the physics definition of power.

Why the others are wrong:

• A: Measuring cylinder assesses volume (e.g., steam), thermometer measures temperature—irrelevant to mechanical work or time.
• B: Measuring cylinder is unnecessary for power; metre rule is useful but incomplete without time measurement.
• D: Stop-watch measures time but thermometer only checks temperature, omitting distance for work.

Final answer: C