Final answer:
Mary can use a ruler to measure the dimensions of an object with a regular shape. From these measurements, Mary can calculate the object's volume, which is a necessary component for determining density when combined with the object's mass.
Step-by-step explanation:
Mary is investigating the densities of objects and considering which measurements she can take using a ruler. A ruler can be used to measure the dimensions of an object, which are then used to calculate the object’s volume if the object has a regular shape. For example, the volume of a rectangular block can be found by measuring its length, width, and height and then using the formula Volume = length × width × height.
Thus, a ruler can provide the necessary data to find the volume of objects with geometrically simple shapes. When asked to rank the densities of objects, Mary would first need to measure their masses using a balance and then measure their volumes using a ruler for objects with regular shapes or by water displacement for irregularly shaped objects. To find density, she would divide each object’s mass by its volume. This means she can use a ruler to help calculate densities as long as she can accurately measure the object's volume with it.
To conclude, in Mary’s examination of object densities, she can certainly use a ruler to gather measurements required to calculate the volume component of density, provided the objects are of regular, measurable shape.