Question

A certain block of plastic is 0.6 as dense as water and therefore floats in water. What weight of water will be dill be displaced by a 100-kg of a floating block of this plastic.

Answer 1

Density=mass/volume

Answer 2

halp?

Answer 3

ok so buoyancy force is equal to the force (or weight) of a floating object or equal to the weight of the total water displaced

therefore: if a 100kg block is floating you know it must have displaced 100kg of water because it is floating so the water's buoyancy force counteracts the gravitational force...therefore the weight of water displaced is (9.8(or 9.81 depending on book)) (100 kg) = 980N

to find the total volume of the block you must find the density by multiplying density of water by .6 density of water is 1000 kg per m^3 therefore the density of the plastic is 600 kg per m^3

density = mass/volume therefore 600 = 100/volume volume = .1666667 m^3 so you need to find the total buoyancy force the water would have to submerge it and subtract the gravitational force from that.

as described above buoyancy force is equal to the weight of water displaced. therefore to find the buoyancy force on the submerged block we multiply the weight of the water per meter cubed by .1666667 1000(9.8(or 9.81 depending on book)) (.1666667) = 1633.333 N

because we are pushing it down we are working with the gravitational field so we subtract the gravitational force that is already there from the total force needed to submerge it because again gravity wants to pull it down so both are in the same direction (or you could add both downward vectors with the equation 980 + x = 1633.333

therefore the total force required to submerge it is 653.33 N ...hope i helped you understand buoyancy force :)