# Homework Help: Buoyany and change in volume underwater

1. Apr 23, 2012

### sweetpete28

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??

2. Apr 23, 2012

### Staff: Mentor

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.)

3. Apr 23, 2012

### sweetpete28

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?

4. Apr 23, 2012

### Staff: Mentor

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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