How is the efficiency of a machine calculated?

The efficiency of a machine is calculated using the formula that compares the useful work output with the total work input. The correct approach involves taking the output work, which is the work done by the machine, and dividing it by the input work, which is the energy supplied to the machine. Multiplying this ratio by 100% converts it into a percentage, reflecting how effectively the machine converts the input energy into useful work.

This calculation is crucial because it allows us to assess how well a machine functions. A higher efficiency percentage indicates that a greater proportion of the input energy is being transformed into useful output work rather than being lost to friction, heat, or other forms of inefficiency. Understanding this concept helps in evaluating machine performance and identifying opportunities for improvement in design or operation.

In contrast, other options focus on different aspects of work or force ratios unrelated to calculating efficiency as defined in this context.