When a vehicle is at high altitude (like a hill) it has huge potential energy. as the vehicle comes down the hill, all that energy is lost in the form of heat due to the application of brakes. suggest some way by which this energy can be temporarily stored in some other form and can be reutilized. not only suggest the principle but address the engineering challenges appearing in building such an apparatus that can be fitted in automobiles to achieve this. this will reduce our dependence on the fuel.