Gravitational potential energy (u) depends on three things: the object’s mass (m), its height (h), and gravitational acceleration (g), which is 9.81 m/s2 on earth’s surface: u = mgh energy is measured in joules (j). one joule is equal to one 1 kg•m2/s2. when calculating the energy of an object, it is to convert the mass and height to kilograms and meters. a. what is the mass of the 50-gram car, in kilograms? b. set hill 1 to 75 cm and the other hills to 0 cm. what is the height in meters? c. what is the potential energy of the car, in joules?