In an ideal machine, work input equals work output.

• A. They are not related
• B. Output is greater
• C. They are equal
• D. Input is greater

Answer: (C)

In an ideal machine, energy is conserved because there are no losses to friction, heat, or other non-ideal effects. The work you put in is transferred to the load, so the total input work equals the total output work. Since work is force times distance, an ideal machine can trade force for distance (and vice versa) through mechanical advantage, but the amount of work remains the same. That’s why the correct statement is that they are equal. If output were greater or input greater, it would imply energy creating or vanishing, which doesn’t happen in an ideal machine. Real machines lose some energy to friction, so then input work would be greater than output work, reducing efficiency below 100%.