What does the question mark on the left side of the energy equation represent?

What does the question mark on the left side of the energy equation represent?

• A. Vessel draining time
• B. Flow rate
• C. Vessel volume
• D. Total mass

Answer: (A)

In this energy-related draining problem, the symbol on the left is a time interval—the duration of the draining process. That unknown represents how long the vessel continues to release liquid. Time is what you multiply a rate by to get a total; for example, flow rate (volume per unit time) times draining time gives the total volume that leaves the vessel, and power (energy per unit time) times draining time gives the total energy transferred during the drain. The other quantities listed—vessel volume, flow rate, and total mass—are different kinds of measures and don’t fill the role of that left-hand-side quantity, which is specifically the duration of the drain.

In this energy-related draining problem, the symbol on the left is a time interval—the duration of the draining process. That unknown represents how long the vessel continues to release liquid. Time is what you multiply a rate by to get a total; for example, flow rate (volume per unit time) times draining time gives the total volume that leaves the vessel, and power (energy per unit time) times draining time gives the total energy transferred during the drain. The other quantities listed—vessel volume, flow rate, and total mass—are different kinds of measures and don’t fill the role of that left-hand-side quantity, which is specifically the duration of the drain.