Horsepower measures the rate at which work is done.

• A. Energy
• B. Rate of doing work
• C. Distance
• D. Force

Answer: (B)

Power is the rate at which work is done. Horsepower is a unit that measures that rate. Work is the energy transferred when a force moves an object through a distance, but horsepower tells you how quickly that transfer happens. For example, moving a 100 N weight by 1 meter does 100 joules of work; doing that in 1 second uses 100 watts of power, while doing it in 10 seconds uses 10 watts. Horsepower, defined as about 746 watts (SI) or 550 ft·lb/s (imperial), captures that speed of doing work. This is what sets horsepower apart from energy (the total amount of work available) and from distance or force, which describe how far or how hard, not how fast the work is performed.