The stings vibrates around the air which makes a longitudinal wave
Since the lemon is falling without any air resistance, the only force acting on the lemon is the acceleration due to gravity.
But, since we know that the lemon is falling with a constant speed. There has to be another unknown force to balance the gravitational force. Which has been shown in the freebody diagram
Inefficiency is a big struggle when it comes to renewable resources. A form of energy might take more energy to harness than it provides because the energy might dissipate. Energy transformation is never 100% conversion. Some of the energy dissipates in the form of heat.
The answer to this question is that work is defined as the change in energy. It measures the change in energy. W = ΔE.