One horsepower equals ______ foot-pounds per second.

• A. 540
• B. 550
• C. 600
• D. 650

Answer: (B)

Power is the rate at which work is done, and work in customary units is force times distance (pounds times feet). One horsepower is defined as the rate of doing 550 foot-pounds of work in one second. In practical terms, that means lifting 550 pounds by 1 foot, or moving 1 pound a distance of 550 feet in one second, all in one second. This standard value comes from James Watt’s original comparison of engines to draft horses. So the exact conversion is 1 horsepower = 550 foot-pounds per second.