Asubmerged submarine alters its to rise or fall in the water.

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Submarines use buoyancy by filling ballast tanks up with water. When they are filled with water, they are more dense than the surrounding water, so they are able to sink. If they want to rise, they fill these tanks up with air so that the density is less than the water it surrounds. 
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D. 39 N m

Explanation:

m = mass of the weight used in crossfit workout = 7.0 kg

Force due to the weight used is given as

F = mg

F = (7.0) (9.8)

F = 68.6 N

d = distance of point of action of weight from shoulder joint = 0.57 m

τ = Torque about the shoulder joint due to the weight

Torque about the shoulder joint due to the weight is given as

τ = F d

Inserting the values

τ = (68.6) (0.57)

τ = 39 Nm