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.) A) +40.0 ml B) -40.0 ml C) -25.2 ml D) 0 ml E) +25.2 ml

Question

Quizplus · Accepted Answer

When the solid aluminum bar is floating on the water, its weight is equal to the weight of the water it displaces. Since the bar has a mass of 40 g, it displaces 40 ml of water, which explains why the water level reads 60 ml (initial volume) instead of 100 ml (total volume of the beaker).

When the aluminum bar sinks to the bottom, it adds its volume to the water, but also adds its weight. The weight of the aluminum bar is 2.7 g/cm3 x (40/grams/2.7) cm3 = 14.81 g. Therefore, the total volume of water + aluminum is 60 ml + (40 ml - 14.81 ml) = 85.19 ml.

The change in volume is therefore: 85.19 ml - 60 ml = -25.19 ml, which corresponds to answer C (-25.2 ml, rounded to one decimal point).

A Beaker Is Filled with Water