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A block of wood is held half immersed in the water. When released, it submerged to a greater degree but remained afloat. When the block was initially released, which of the following must have been true?
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Correct Answer: C. Initial buoyant force < maximum buoyant force
Tricky! You must recognize that the half immersed block would submerge as long as its density is greater than 1/2 the density of water or a specific gravity of 0.5. Thus this block may: (i) have a specific gravity between 0.5 and 1.0 (which means the block’s density would be less than that of water); or (ii) it could have a density equal to that of water; but (iii) it could NOT have a density greater than that of water (this would make it sink to the bottom but the question says that it remains afloat so (iii) is not possible): nonetheless, it would submerge from a position of being held half immersed [thus answer choice B. is not the best answer because of the preceding points (i) and (ii)]. When the block sinks, it will certainly displace more water than it did initially; therefore, the buoyant force increases to its maximum. {cf. Archimedes Principle}
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