Which statement is true about horsepower-hours?

• A. One horsepower-hour equals approximately 2.684 × 10^6 joules
• B. One horsepower-hour equals one kilowatt-hour
• C. One horsepower-hour equals one joule
• D. One horsepower-hour equals one watt-hour

Answer: (A)

A horsepower-hour is energy obtained by a power of one horsepower sustained for one hour. Since 1 horsepower is about 746 watts and 1 hour is 3600 seconds, the energy is 746 W × 3600 s ≈ 2,685,600 joules, which is about 2.684 × 10^6 J. This matches the statement exactly, making it the correct choice.

To put it in context, 1 horsepower-hour is also 746 watt-hours (since power in watts times hours equals energy in watt-hours), which is about 0.746 kilowatt-hours. That shows why it isn’t equal to 1 kilowatt-hour, nor to 1 joule or 1 watt-hour.