Domestic refrigerators are designed with the cooling compartment at the top to cool the air inside the cabinet.
The passage below explains the movement of air inside a refrigerator.
Choose the correct words from the box to complete the passage. Each word may be used once, more than once, or not at all:
conduction, contracts, faster, expands, increases, convection, decreases, slower
"Air is cooled by the compartment at the top and the air molecules move __________ .
The air __________ as the molecules pack closer together.
The density of the air __________ and the cold air sinks.
Warm air rises from the bottom of the fridge to replace it and the process continues as a __________ current."
An electric water pump is used to lift a mass of 250 kg250\text{ kg}250 kg of water vertically upwards by a height of 18 m18\text{ m}18 m from a low-level reservoir to a storage tank.
State the equation linking gravitational potential energy (GPE), mass, ggg, and height.
Calculate the gain in GPE when the water is lifted 18 m18\text{ m}18 m.
State the work done in lifting the water.
