ICSE Class 6 Answered

Work done by a machine upon performing certain amount of work on the machine (work input) is called work output. 

Thus, it can be said that the machine does a work when certain amount of work is done on it. 

Thus, work output of machine is equal to work input. 

But in reality, it is not true. Because, the work done on machine (work input) is utilized to overcome the frictional force between the moving parts of the machine. Thus, in reality work output is less than the work input.