Power as rate of work

Steps:

• Recall the physics definition: power measures how quickly work is done.
• Identify the formula: power P equals work W divided by time t, or P = W/t.
• Compare options: look for phrasing that matches "work divided by time."
• Select the precise term: "per unit time" indicates division by time interval.

Why D is correct:

• Power is defined as work done per unit time, matching the formula P = W/t, where unit time is any consistent interval like seconds.

Why the others are wrong:

• A: Specifies "one second," limiting to a fixed time, not general unit time.
• B: "In unit time" implies total work over time, not the rate.
• C: "Per second" restricts to seconds only, ignoring other units.

Final answer: D