Question

A 10cm×10cm×10cm wood block with a density of 750 kg/m3 floats in water. What is the distance from the top of the block to the water if the water is fresh?

If it's seawater? Suppose that ρ=1030kg/m3.

Express your answer to two significant figures and include the appropriate units.

Answer 1

In fresh water (density of 1g/cc.), the block will float with 10- (10 x 0.75) = 2.5 cm. above water.

The salt water one is tougher.

Block density is 750 kg/m^3, which equates to 0.75 g/cc.  

Block volume = (10^3) = 1,000 cc

Its mass is (1,000 x 0.75) = 750 grams

It will displace its own mass of water when it floats

The volume of water displaced = (750 /1.030) = 728.16 cc

The block area = (10 x 10) = 100 cm^2.

Height out of water = 10cm - (728.16/100) = 2.72 cm

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