One possibility for a low-pollution automobile is for it to use energy stored in a heavy rotating flywheel of mass 240 kg, and should be able to travel 300 km (300,000 m) without needing a flywheel "spinup." Make reasonable assumptions (avg. frictional retarding force 500 N, 20 acceleration periods from rest to 90 km/h or 25 m/s, equal uphill and downhill --assuming during downhill, energy can be put back into the flywheel), and show that the total energy needed to be stored in fly wheel is about 1.6 x 10^8 J. I need help to start this proof. Do you use K_i + U_i = K_f + U_f? What do I do from here? Thanks for any pointers.