Competency #4
Answer and Explanation
First we need to identify the forces acting on each object. Both objects have mass, so we need to include a force of gravity (Fg) for each. Both objects are submerged in water, so we need to include a force of buoyancy (Fb). In addition, since the child sank, and is resting on the bottom, there will be a force from the tub (Ftub). There is no F tub for the boat, because it is floating on the surface of the water.
To draw the force diagram we make some assumptions:
- Volume of child submerged is greater than the boat, so the buoyant force for child is greater.
- Mass of child is greater than the boat, so force of gravity for child is greater.
The magnitude of the Ftub is enough so that there is no net force acting on the child.
Note that the volume of the child submerged is less than the total volume of the child.
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