Delivery trucks that operate by making use of energy stored in a rotating flywheel have been used in Europe. The trucks are charged by using an electric motor to get the flywheel up to its top speed of 198π rad/s. One such flywheel is a solid, homogeneous cylinder with a mass of 530 kg and a radius of 1.0 m. If the truck operates with an average power requirement of 8.5 kW, how long can it operate between chargings? Just a push in the right direction, i've written out so many formulas relating to rotation and Power/Work. And i haven't found a starting point.