Question

A motor with an input power of 100 Watts is connected to a flywheel . How long in units of hours must the motor operate to transfer 300000 joules to the flywheel assuming the process is 80% efficient

Answer 1

Power is the rate of work done given by dividing work done by time.Efficiency is the ratio of work output to work input
power input= 100 watts
power output = x
efficiency= 0.8 
thus 0.8 = x/100, therefore x = 80
power is given by energy times time
hence time = 80/300000 = 0.00026 seconds 
Time in hours = 0.00026/360 = 7.407 x 10 ∧7 hours