Final answer:
Using salt water instead of fresh water to measure a patient's density affects the results by providing an overestimated density value due to the higher buoyancy in salt water, resulting in less of the body being submerged.
Step-by-step explanation:
If you were to unknowingly use salt water (rho = 1025 kg/m³) in place of fresh water to measure a patient's density, this would result in the patient appearing to have a higher density than they actually do. To understand this, let's consider an example where a body with a density of 995 kg/m³ is submerged in freshwater and salt water. In freshwater, the fraction of the body submerged is equal to the body's density divided by the density of freshwater (1000 kg/m³). Therefore, 995/1000 or 99.5% of the body would be submerged. In salt water, which has a higher density (1027 kg/m³), the ratio becomes 995/1027, meaning about 96.9% of the body would be submerged.
Thus, using salt water instead of fresh water causes less of the body to be submerged due to salt water's greater buoyancy effect. Someone's density would be overestimated when using salt water. This can be crucial for medical applications, where accurate density measurements are necessary for diagnoses or treatments.