Multiple Choice Question Mechanical efficiency can be defined, in terms of power, as the: ratio of output power to input power. ratio of input power to output power. ratio of the difference of the input and output power to the input work.

To determine the correct definition of mechanical efficiency in terms of power, let's analyze the options provided: 1. **Ratio of output power to input power.** - This definition aligns with the standard definition of mechanical efficiency, which measures how effectively a machine converts input power into useful output power. 2. **Ratio of input power to output power.** - This definition is incorrect because it would yield a value greater than 1 for efficient machines, which does not represent efficiency. 3. **Ratio of the difference of the input and output power to the input work.** - This definition is also incorrect as it does not accurately represent the concept of efficiency, which is typically a straightforward ratio of output to input. Based on this analysis, the correct answer is: **Ratio of output power to input power.**