Question

What is the efficiency of a machine that miraculously converts all the input energy to useful output energy?

Answer 1

A perfectly efficient machine can only be 100% efficient. 

Answer 2

Answer: 100%

Step-by-step explanation:

Efficiency = output/input = 100/100 x 100 = 100% efficient

Machines are not 100% efficient because some of the work done by a machine is used to overcome friction. So work output is always less than work input.

Work: Done by machines is calculates as Mechanical Efficiency which is Work Output divided by Work Input.