Final answer:
Measuring the melting point of a substance is not a cost-effective method to identify if the white dust in a car is aluminum oxide. Other methods such as chemical tests or spectroscopic analysis would be more suitable.
Step-by-step explanation:
To identify if the white dust in a car is aluminum oxide, measuring the melting point of the substance would not be a cost-effective method. This is because aluminum oxide has a very high melting point of about 2054°C. It is not practical or cost-effective to measure such high temperatures in order to identify the substance. Instead, other methods such as chemical tests or spectroscopic analysis would be more suitable for identifying aluminum oxide.