Physics!!! plz help=( ty^-^?

Question

1)Calculate the water pressure at the base of Hoover Damn. the depth of water behing the dam is 220m.(Neglect the pressure due to atmosphere.)
2)The top floor of a building is 30 m above the basement. Calculate how much greater the water pressure is in the basement compared with the pressure at the top floor.
3)An 8.6-kg piece of metal displaces 1 liter of water when submerged. Calculate its density.
4)A 4.7-kg piece of metal displaces 0.6 litrt of water when submerged. Calculate its density.
5)A one-cubic centimeter cube has sides 1 cm in length. What is the length of the sides of a cube of volume two cubic centimeters?
6)Consider eigth one-cubic-centimeter sugar cubes stacked two-by-two to form a single bigger cube.What will be the volume of the combined cube?How does its surface area compare to the total surface area of the eigth seperate cubes?

Answer 1

For 1 and 2:
The pressure exerted by a column of liquid = mass of liquid m * g / cross-sectional area A The mass = cross-sectional area A * height h * density d, so we have
P = m * g / A (1) (m in kg, g in m.s-2, A in m2)
m = (A * h) * d (2) (A in m2, h in m, d in kg.m-3)
P = h * d * g. (h in metres, d in kg.m-3, g in m.s-2)
In other words, the area of the column of liquid does not matter. This is what you need to know to calculate the pressure at the bottom of a column of liquid.

For 3 and 4:
The volume of water displaced when an object is completely submerged in water is equal to its own volume. Density = mass / volume. Usually written in kg.m-3 as opposed to kg.l-1, so you will need to convert litres to cubic metres.

For 5 and 6:
Volume of rectangular solid = length * breadth * height.
Total surface area of a solid = the sum of the areas of each of its faces.

Hope that helps.

Answer 2

First and foremost, blackholes are NOT formed when matter is compressed to a point of singularity. They have finite radius and they have definite mass (and spin and charge). And the universe cannot come from any sort of blackhole we know of simply because we know the mass/energy of the universe and we know that of a blackhole and there is a huge mismatch (universe is much much much heavier than the heaviest blackhole we know about). Moreover, even though we might not know exactly the laws of physics inside the radius of the blackhole, we know that the mass/energy of it does not vanish inexplicably ... conservation laws keep an account of them, so the mass inside a blackhole cannot just stream into other universes, so to speak. Thirdly, expansion of our universe is not due to addition of new mass (you seem to imply something like that ... 'sucking from ... adding to ours') ... total mass remain the same and as it expands, that means the density decreases continuously ... and that's another indication that our universe was not created by siphoning matter from a huge huge blackhole from a different universe having said that, that does not throw away the possibility of multiverse ... in fact existence of multiverse is quite well known cosmology ... but not in the way you are imagining it to be keep up an open mind and keep asking yourself questions ... that's the way to learn (also by working hard with regular course work at the same time :)). best wishes ...