A block and tackle system is used to lift a load of 20X through a vertical height of 10.5m. If the
efficiency of the system is 40%, how much work is done against friction?
work done: loadweight*height
I don't know what you mean by 20x.
work input= workdoneabove/.4
friction= workinput-workdone
= workdone(1/.4 -1)=workdone*.6/.4