Fluid Question and density tension etc.

[amaris]

1)Styrofoam has a density of 300kg/m^3. What is the maximum mass that can hang without sinking from a 40.0 cm-diameter Styrofoam sphere in water?

Found density of styrofoam per cm^3...then got lost

2)A gym is 14.0m high, what is the percentage difference between air pressure at the top of the gym and on the ground of the gym?

no clue whatsoever

3)A 6.00 cm-tall cylinder floats in water with its axis perpendicular to the surface. The length of the cylinder above water is 1.30 cm. What is the cylinder's mass density?

I took the height of the cylinder that was submerged and divided it over the total height to find the volume that was submerged then multiplied that by the density of water -.-

4)2.60 kg rock whose density is 4100 kg/m^3 is suspended by a string such that half of the rock's volume is under water. What is the tension in the string?

somehow or another I arrived at the answer of 25.5, not quite sure how but either way it was wrong.


I know it sounds like you're doing my entire hmwk assignment, but this is merely less than half of what I've done already. :(

need desperate urgent help...

edit: solved the first qn on my own

 

[Hunterbender]

show that you try to solve the problem first

2. look at the psi difference. There is air in the room, so there must be pressure from that at the bottom of the room that doesn't exist at the top

3. Use bouancy force? maybe? Looks promising

4. same as 3.