Question

I would appreciate some help.

A machine has an efficiency of 70%. How much work does the machine do when 20,000 J of work is done on it?

14,000 J
28,600 J
1,400,000 J
2,860,000 J

Answer 1

~its A~ 14,000 joules

Hope I helped :D

Answer 2

You oughtta be able to do this one.

The "efficiency" is just the portion of the input work that
comes out in a useful form.

If the efficiency is 70%, that tells you that however much work
you put INto the machine, the machine will do 70% of that much
work for you at the output side.

Put 20,000 J in ... out comes (0.70) x (20,000 J) = 14,000 J .

What happens to the other 30% of the work you put into it ?
It turns into HEAT. That's why machines always have to be
cooled somehow while they're running.