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An object of mass 3 kg floats motionless in a fluid of specific gravity 0.8. What is the magnitude of the buoyant force? (Use g = 10 m/s2).

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Correct Answer: D. 30N.
Since the object is not moving, its acceleration must be zero, so the net force on it must also be zero. Therefore, the magnitude of the buoyant force upward must equal the magnitude of the weight downward, the specific gravity is extraneous information:
B = w = mg = (3 kg)(10 N/kg) = 30 N
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