Final answer:
The correct answer is c) "Because of air pressure". The limitation to lift water to a higher elevation, such as a third floor, with a pump is due to the maximum height that atmospheric pressure can support a column of water, which is about 10.3 meters. Pumps cannot create a strong enough vacuum to overcome atmospheric pressure beyond this limit in standard conditions.
Step-by-step explanation:
The question "Why can't you use a pump to lift water to the third floor?" refers to the limitations imposed on moving fluids, such as water, through a pump to higher elevations. Considering the provided options, the most scientifically accurate reason is c) "Because of air pressure". Air pressure, also known as atmospheric pressure, is a fundamental force in fluid dynamics and influences the extent to which water can be pumped to higher levels.
Atmospheric pressure exerts a force on top of bodies of water. Under normal atmospheric conditions, the maximum height to which water can be lifted by creating a vacuum above the water is approximately 10.3 meters, or about 34 feet, due to the fact that atmospheric pressure can only support a column of water that high. This value assumes standard atmospheric pressure at sea level and can vary with different atmospheric conditions. Trying to pump water higher would require overcoming the ambient atmospheric pressure, which a standard pump is typically not capable of, as it cannot create a suction strong enough to lift water beyond this limit without risking cavitation.
An additional consideration comes from Pascal's principle, which states that a change in pressure applied to an enclosed fluid is transmitted undiminished to every portion of the fluid and the walls of its container. Thus, in the case of an open system, like pumping water to a building's third floor, the pressure due to the weight of the water and the atmospheric pressure must be taken into account. The combined pressures would require a more robust pump or a series of pumps to achieve the necessary lift.