Final answer:
Work is done when an exerted force causes motion in the same direction. Simple machines change applied force but not the total work done.
Explanation:
Work is done when a force is exerted, and there is motion or displacement in the direction of the force. Simple machines like levers and pulleys can change the amount of force applied, but they cannot change the amount of work done.
The efficiency of a simple machine is always less than 100% due to energy losses, such as heat generated by friction. Efficiency is calculated as the output work divided by the input work, usually expressed as a percentage.
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