Which aspect of a simple machine is represented by the ratio work output to work input?

• A. Power expended
• B. Efficiency
• C. Actual mechanical advantage
• D. Ideal mechanical advantage

Answer: (B)

The idea being tested is how well a simple machine uses input energy to do useful work. The ratio of work output to work input is efficiency, which shows what fraction of the input energy actually becomes useful work. In real machines, some energy is lost to friction, heat, and other losses, so efficiency is less than 1 (often written as a percentage). For example, if you input 100 joules and obtain 80 joules of useful work, the efficiency is 0.8 or 80%. The other concepts describe different ideas: power expended is about the rate at which work is done, not the energy conversion; actual mechanical advantage compares output force to input force; ideal mechanical advantage is the theoretical force ratio with no losses.