Final answer:
To measure his weight, a student of mechanics should use a bathroom scale, which calculates mass based on Earth's gravity from the measured weight.
Step-by-step explanation:
If a student of mechanics wishes to weigh himself but has access to only a bathroom scale, the appropriate tool to use would be the bathroom scale. Bathroom scales measure weight, which is the downward force due to gravity, and then calculate and display mass based on Earth's gravity. When a person stands on the bathroom scale, the spring inside compresses proportional to the weight exerted, providing a measure of one's weight. This is usually given in units of pounds or kilograms depending on the location. If the same scale was used on the moon, it would detect a different weight because the moon's gravitational force is different from Earth's, but it would be calibrated to still display your mass on Earth.
For example, when measuring the weight of a violin, a scale or balance would be the appropriate tool to use. Likewise, a scale would also be used to weigh an apple or a bag of flour. These examples illustrate how vital it is to select the proper tool for accurate measurement in mechanics.