Question

efficiency of machines quick check
1000 joules of energy are put into a pulley system, and 400 joules come out. what does the law of conservation of energy imply about the lost
the lost energy cannot be recovered.
the pulley system could be improved to conserve some of the lost energy.
the lost energy is caused by friction.
the lost energy is not truly lost, but it changed into a different form.

Explanation:

The Law of Conservation of Energy states that energy cannot be created or destroyed, only transformed from one form to another. In a pulley system, when input energy (1000 J) is more than output energy (400 J), the "lost" energy is actually converted into other forms (like heat due to friction, sound, etc.), not truly lost. The first option is incorrect as energy can be recovered in some cases (e.g., converting heat back, though not fully efficient here). The second option is about improving the system, not what the law implies. The third option identifies a cause (friction) but the law's implication is about energy transformation, not the cause. So the correct choice is the one about energy changing form.

Answer:

The lost energy is not truly lost, but it changed into a different form.