5)Efficiency


 * __Efficiency__**
 * The efficiency of a roller-coaster is given by useful energy output / energy input x100%
 * The higher the efficiency, the higher the percentage of GPE converted to KE, which is the useful energy output in this case, while the energy wasted are the thermal and sound energy.
 * Efficiency can be increased by reducing the friction between the wheels of the roller-coaster and the track
 * Calculation of efficiency is important as it lets us know what is the maximum height of the next upward slope the roller coaster can climb, by letting us know how much kinetic energy it has
 * Note that a roller-coaster cannot ever be 100% efficient as some of the GPE is always lost as thermal energy and sound energy