A cargo elevator on Earth (where g = 10 m/s2) lifts 3000 kg upwards by 20 m. 720 kJ of electrical energy is used up in the process. What is the efficiency of this process?

Answer: 83%

Explanation:

Efficiency of the process = work output/work input * 100%

Work input is the energy used up in the process = 720,000Joules

Work output = Force * distance

= (3000*10) * 20

= 600000 Joules

Efficiency = 600000/720000 * 100

= 0.83*100

= 83%