Question

Describe the circumstances for which the output work would equal the input work in a machine.

Answer 1

machine must have an 100% efficiency rating

Answer 2

It may be a friction-less machine. You would have to double check on that.

Answer 3

i believe aidanbk has the best answer, but remember that only in completely ideal and hypothetical situations would a machine have a 100% efficiency, because some of the work put in will be lost to heat, and that is only one example as to how some energy would be lost