Efficiency

Efficiency defines how much useful energy a machine produces from the energy given into it. Simply put, efficiency is the ratio of useful energy to total energy

Calculating Efficiency §

$$Efficiency\%=\frac{UsefulEnergy}{TotalEnergy}\times 100\%$$

• Useful energy refers to energy generated which is related to the system’s operation. For example, useful energy from a heating system would be heat (thermal) energy, but useful energy to a car would be movement (kinetic) energy
• Total energy refers to all the energy used by the system. As some energy is always wasted, usually due to friction and sound, it is impossible to have a 100% efficient system.

However, in VCAA questions, all systems are ideal unless stated otherwise, so assume all machines to have 100% efficiency.

VR, MA & Efficiency §

Efficiency can also be calculated via Mechanical Advantage & Velocity Ratios. As mentioned, Efficiency is the ratio of the useful energy to total energy. Using the formula for work, we can derive an efficiency formula using MA & VR.

$Effiency=\frac{UsefulEnergy}{TotalEnergy}$

$=\frac{LoadEnergy}{EffortEnergy}=\frac{F_{Load}\times d_{Load}}{F_{Effort}\times d_{Effort}}$

$=MA\times \frac{1}{VR}=\frac{MA}{VR}$