A team of students builds a lever as a science project. They expend 100 Joules of energy to lift some bricks with the lever. If 60 Joules of energy are applied to the bricks, what is the lever’s efficiency?

Answer 1

Efficiency = (useful energy output / total energy input) * 100%

Useful energy output = work done by lever = 100 Joules
Total energy input = energy applied to bricks + energy lost due to friction or other factors
Total energy input = 60 Joules + (100 Joules - 60 Joules) = 100 Joules

Efficiency = (100 Joules / 100 Joules) * 100% = 100%

Therefore, the efficiency of the lever is 100%. All of the energy input was used for the useful work of lifting the bricks, with no energy lost to other factors. However, in reality, some energy is always lost due to factors such as friction, so 100% efficiency is rarely achievable.