Which statement correctly defines machine efficiency?

Machine efficiency is defined as the ratio of useful work output to total work input. This definition reflects how effectively a machine converts the input energy (or work) it receives into useful work output. In practical terms, it is measured as a percentage, and a higher efficiency indicates that more of the input energy is converted into useful work rather than being lost to other forms such as heat, friction, or other inefficiencies.

This approach captures the overall performance of the machine and is essential for evaluating its effectiveness in various applications. Understanding machine efficiency is crucial in mechanical engineering and design since it helps in optimizing performance and reducing energy consumption.

The other statements do not accurately describe machine efficiency. For instance, it is impossible for machine efficiency to exceed 100% because this would imply that a machine is producing more work than the energy it receives, which violates the principles of conservation of energy. Calculating work input divided by work output does not provide a valid measure for efficiency since it essentially inverts the definition and does not account for losses. Finally, considering only mechanical losses does not cover the full scope of efficiency, which involves all forms of energy losses, not just mechanical ones.