Final answer:
Under constant efficiency and specific heat capacity, doubling the mass of water and tripling the falling height results in a temperature change of 2.1°C.
Step-by-step explanation:
The question involves the concept of energy conversion from gravitational potential energy to thermal energy and the specific heat capacity of water, which is how much energy is required to raise the temperature of a certain amount of substance. In the first scenario, dropping a cylinder containing 2 kg of water from a height of 250 m results in a temperature increase of 1.4°C. When the mass of the water is doubled, the same amount of energy spread over more mass will lead to a smaller temperature change, assuming efficiency and specific heat capacity remain constant. Since the mass is doubled and the height is tripled (750 m as opposed to 250 m), the new temperature change will be 1.5 times the original change, which was 1.4°C, giving a new temperature increase of 2.1°C.