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6) Since potential energy is directly proportional to height, the potential energy of this car would be doubled 7) Since potential energy is directly proportional to weight, the potential energy of the car would be doubled when it is twice as massive as the other. 8) The book gains 4 joules of potential energy when it is elevated 4m. When the book is elevated 8m, it gains 8 joules of potential energy. 9) If the car speeds up until it is going four times as fast, the kinetic energy is sixteen times in comparison. 10) If the car moves three times as fast, then the kinetic energy is nine times, therefore it takes nine times as much distance to stop.