One horse produces 15 hps

The power output of your car’s engine can be measured in different ways, but the most common is in horsepower. An average horse achieves a maximum of 15 hp. Mechanical horsepower, also known as imperial horsepower, is the measurement invented by James Watts and is approximately equivalent to 745.7 watts of power. So why do we horsepower as a measurement?
In short – marketing. Before the steam engine, one or more horses were often used by farmers. In order to sell steam engines, it was important to describe them in terms that the customers would understand.
A group of researchers in Mexico calculated the maximum power that Usain Bolt reached during his 9.58s world record 100m run in the World Championships in Berlin in 2009. According to their calculations, Bolt reached 2619.5 watts which is equal to 3.5 HP.

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