Question

The efficiency of a practical simple machine can never be 100%​

Answer 1

True

because output of a machine is always less than input

Answer 2

Compound machines have low mechanical efficiency is because they have more moving parts and thus more friction to overcome.

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

A machine cannot be 100 percent efficient because output of a machine is always less than input. A certain amount of work done on a machine is lost to overcome friction and to lift some moving parts of the machine.