To determine athletes body fat, there are weighed first in air and then again while they are completely underwater. It is found that one athlete weighs 690 N when weighed in air and 42 N when weighed underwater. What is the average density

1065 Kgm-3

Explanation:

We can determine the relative density of the athlete from the formula;

Relative density of athlete = weight of athlete in air/upthrust on athlete

Since weight of athlete in air = 690 N

Weight of athlete in water = 42 N

Upthrust on athlete = weight in air - weight in water

Upthrust on athlete = 690 N - 42 N = 648 N

Relative density of athlete = 690 N / 648 N

Relative density of athlete = 1.065

Therefore, average density of the athlete = relative density * density of water = 1.065 * 1000 Kgm-3 = 1065 Kgm-3