Which statement best defines energy in relation to power and time, and its unit?

Which statement best defines energy in relation to power and time, and its unit?

• A. Mass times acceleration
• B. Power times time in kilowatt-hours
• C. Force times distance
• D. Speed times distance

Answer: (B)

Energy is the amount of energy transferred or stored, and it equals the rate of transfer (power) multiplied by the time over which that transfer occurs. In formula terms, E = P × t. Using kilowatts for power and hours for time gives energy in kilowatt-hours, which is why this unit is commonly used for electrical energy. If you used watts and seconds, energy would be in joules. The other expressions describe different physical quantities: mass times acceleration is force, force times distance is work (a form of energy transfer), and speed times distance isn’t a standard measure of energy.

Energy is the amount of energy transferred or stored, and it equals the rate of transfer (power) multiplied by the time over which that transfer occurs. In formula terms, E = P × t. Using kilowatts for power and hours for time gives energy in kilowatt-hours, which is why this unit is commonly used for electrical energy. If you used watts and seconds, energy would be in joules. The other expressions describe different physical quantities: mass times acceleration is force, force times distance is work (a form of energy transfer), and speed times distance isn’t a standard measure of energy.