Buoyany and change in volume underwater

AI Thread Summary
Breathing deeply alters a swimmer's body volume, affecting buoyancy underwater. The apparent weight is calculated as the weight in air minus the buoyant force, which is determined by the weight of the displaced fluid. To find the change in volume when the swimmer inhales, one can set up the equations without needing the weight in air. In a related problem, a rectangular block of wood floating in water is pushed deeper when a dog steps on it, requiring the calculation of the dog's mass based on the change in submerged depth. The solution involves setting up force equations while assuming the block remains upright.
sweetpete28
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By breathing in deeply, you can change volume of your body. Suppose a swimmer underwater weighs wf = 23.4 N with his lungs full, and we = 48.0 N with lungs empty. Find change in body volume when swimmer inhales.

I know the apparent weight = weight in air - buoyant force and buoyant force = weight of displaced fluid = desnity of liquid x g x volume but how do I solve for the change in volume without weight in air??
 
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Just set up the equations and solve for the change in volume. You won't need the weight in air. (Note that you are finding the change in volume, not the volume.)
 
Yup! Just got that one...here is last one I need to finish in 20 min...

A rectangular block of wood (M = 260 kg) floats on a calm fresh water lake with do = 12.6 cm below the water. When a dog steps on the block, the block is pushed downward so that now it floads with d = 15.9 cm beneath the water. Find the mass of the dog.

any suggestions?
 
Just set up your force equations. Assume that the block remains upright and has some cross-sectional area A. (You won't need a numerical value.)
 

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