If a machine requires an input of 5000 Joules of input to do 2500 Joules of work, what is the efficiency of the machine?
Efficiency = Output work/Input work x 100%
a. 150%
b. 80%
c. 50%
d. 100%
Efficiency = 2500 Joules / 5000 Joules x 100% = 50%
Therefore, the correct answer is c. 50%.