Use the figure to the right to answer the next problem. A beaker is filled with water.A small plastic container contains a solid bar of aluminum,which has a mass of 40 g,and is placed on the water so that it floats.The water level reads 60 ml.Next,the bar of aluminum is taken out of the container and placed in the water so that it sinks to the bottom.
-By how much does the water level change? (density of Al is 2.7 g/cm³)

Question

Use the figure to the right to answer the next problem. A beaker is filled with water.A small plastic container contains a solid bar of aluminum,which has a mass of 40 g,and is placed on the water so that it floats.The water level reads 60 ml.Next,the bar of aluminum is taken out of the container and placed in the water so that it sinks to the bottom.

-By how much does the water level change? (density of Al is 2.7 g/cm³)

Quizplus · Accepted Answer

When the bar of aluminum is floating, it displaces an amount of water equal to its own weight (40g) in order to be buoyant. Since the density of aluminum is less than water, it floats. This means that the water level rises by 40 ml (volume of water displaced).

When the bar of aluminum is fully submerged at the bottom, it displaces an amount of water equal to its own volume. The volume of the aluminum bar is mass/density = 40g / 2.7 g/cm^3 = 14.8 cm^3. This means that the water level rises by 14.8 ml.

Therefore, the total change in water level is 40 ml (when the bar is floating) plus 14.8 ml (when the bar is submerged) = 54.8 ml. However, we are only interested in the difference in water level when the bar is submerged, so the answer is 54.8 ml - 40 ml = 14.8 ml.

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