Final answer:
The question involves determining the percentage of cavity inside a body based on its weight in air and in water, as well as its specific gravity. The calculation shows that the body's weight loss in water is due to the water displaced by the non-cavity volume of the material, and given the specific gravity, there are no cavities in the body.
Step-by-step explanation:
When a body weighs in air and its reading is 10g, and when it weighs in water, its reading is 8g, we can determine the % of cavity inside the body using the principle of buoyancy and the concept of specific gravity. The specific gravity of the material of the body is given as 5, which is a ratio of the density of the material to the density of water (1 g/cm3 at 4°C).
First, we calculate the loss of weight in water, which is the difference between the weight in air and in water, hence 10g - 8g = 2g. This weight loss is equal to the weight of the water displaced by the volume of the body that is not cavity. The volume of water displaced in cm3 (which is equivalent to its weight in grams in this case because the density of water is 1 g/cm3) is therefore 2 cm3.
Since the specific gravity of the material is 5, the true volume of the material without any cavities would be the weight in air (10g) divided by the specific gravity (5), yielding a volume of 2 cm3. However, the body actually displaces 2 cm3 of water while only weighing 10g due to the cavity. This indicates that the cavities within the body must have a volume of 0, because otherwise, the body would've displaced more water. Therefore, there is no cavity inside the body. If there were any cavities, the displaced volume of water would have been greater than the volume of material calculated based on the specific gravity, leading to a different calculation for the percentage of cavities.