Horsepower is defined as?

• A. A unit of pressure
• B. The power rating of an electric motor
• C. The force to lift a horse at a trot
• D. The amount of work a horse could do in one second; one horsepower equals 550 foot-pounds per second, or 33,000 foot-pounds per minute

Answer: (D)

Power is the rate at which work is done. Horsepower captures how quickly energy can be transferred or used. It was defined to reflect the work a horse could do in a second: 550 foot-pounds of work per second, which equals 33,000 foot-pounds per minute. That same value is about 745.7 watts. So horsepower isn’t a unit of pressure, nor simply the rating of an electric motor, and it isn’t the force required to lift a horse at a trot. It specifically measures the speed of doing work—how much work is accomplished per unit of time.