The unit of energy equivalent to the ability to do work is called?

The unit of energy equivalent to the ability to do work is the Joule. The Joule is defined as the amount of energy transferred when a force of one newton is applied over a distance of one meter. This concept ties directly into the work-energy principle in physics, where work is defined as the process of energy transfer that occurs when an object is moved over a distance due to an applied force.

The Newton, on the other hand, is a unit of force, not energy. Although it plays a critical role in understanding the forces involved in doing work, it does not measure energy itself. Similarly, the Watt is a unit of power, which is defined as the rate at which work is done or energy is transferred over time, thus distinguishing it from the stationary measurement of energy. Lastly, horsepower is a unit of measurement for power typically used to describe the output of engines, but like the Watt, it measures the rate of work rather than energy itself.

The Joule, therefore, is the correct answer as it directly represents the ability to do work through the transfer of energy.