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Hydrostatic weighing is a technique used to determine an individual's overall body density. The weight of the individual is measured when their body is completely submerged in water. Because the volume of air in the respiratory system affects the measured underwater weight, the individual must exhale completely before entering the water. However, residual volume, the volume of air that always remains in the respiratory system, must also be accounted for.By comparing an individual's in-air weight to their underwater weight, their total body volume can be determined. The density of the body D_b excluding any air in the respiratory system is calculated with the in-air mass of the individual m_air, the individual's total body volume V_total, and an estimate of residual volume V_res by:
Db=mairVtotal-VresEquation 1Body density can be used to calculate an individual's body fat composition, the percentage of total body mass that is made up of fatty tissue. Human fatty tissue has an average density of 0.9 kg/L, and the density of water is 1 kg/L. The acceleration due to gravity is 10 m/s².
Adapted from Siri, WE, Body composition from fluids spaces and density. Nutrition 1956 Springer Nature.
-An object with the same density as water is stationary and suspended in a container filled with water. Ignoring the effects of fluid friction, what will happen to the object after a downward force is momentarily applied?

Question

Passage
Hydrostatic weighing is a technique used to determine an individual's overall body density. The weight of the individual is measured when their body is completely submerged in water. Because the volume of air in the respiratory system affects the measured underwater weight, the individual must exhale completely before entering the water. However, residual volume, the volume of air that always remains in the respiratory system, must also be accounted for.By comparing an individual's in-air weight to their underwater weight, their total body volume can be determined. The density of the body D_b excluding any air in the respiratory system is calculated with the in-air mass of the individual m_air, the individual's total body volume V_total, and an estimate of residual volume V_res by:

Db=mairVtotal-VresEquation 1Body density can be used to calculate an individual's body fat composition, the percentage of total body mass that is made up of fatty tissue. Human fatty tissue has an average density of 0.9 kg/L, and the density of water is 1 kg/L. The acceleration due to gravity is 10 m/s².
Adapted from Siri, WE, Body composition from fluids spaces and density. Nutrition 1956 Springer Nature.
-An object with the same density as water is stationary and suspended in a container filled with water. Ignoring the effects of fluid friction, what will happen to the object after a downward force is momentarily applied?

Quizplus · Accepted Answer

11ecba2d_12f7_ff92_a3bf_c79fbd1458f0_MD0008_00 An object that is suspended (submerged and stationary) is neither sinking nor rising because it has the same density as the surrounding fluid. Therefore, the initial net force on the object is zero, and the object's initial velocity is zero. When a downward force is applied to the object, the net force on the object is downward. The object will sink, and its velocity in the downward direction increases with time (accelerates) as described by Newton's second law (F = ma). The moment after the applied force is removed, the net force acting on the object returns to zero (ignoring fluid friction). In the absence of a net force, an object at rest (velocity = 0 m/s) will stay at rest, and an object in motion at a given velocity will stay in motion at the same velocity (Newton's first law) (Choice B). Therefore, the object will continue to sink at a constant velocity. (Choice C) An object that experiences a net force of zero will remain at its current velocity; it does not imply that the object will stop moving. (Choice D) A net force pointing upward would be required to return the object to its initial position. After the applied force is removed, the net force returns to zero. Educational objective: When a mass experiences a net force, the mass will accelerate in the direction of the force (F = ma). When no net force acts on an object, its velocity remains unchanged. Therefore, an object will accelerate to a velocity when a force is applied and will continue at the same velocity after the force is removed.

Passage Hydrostatic Weighing Is a Technique Used to Determine an Individual's