Physics Stuff?

Question

I don't need the questions done, just some sort of idea of how to start them. Any help would be appreciated.

Oxygen at pressures much greater than 1 atm is toxic to lung cells. Assume that a deep-sea diver breathes a mixture of oxygen and helium (He). By weight, what ratio of helium to oxygen must be used if the diver is at an ocean depth of 47.0 m?
Round your answer to three significant figures

In a period of 1.60 s, nitrogen molecules strike a wall of area 4.2 cm squared If the molecules move at a speed of 340 m/s and strike the wall head-on in elastic collisions, what is the pressure exerted on the wall? (The mass of one molecule is 4.68 x10^-26)
Round your answer to three significant figures.

Answer 1

You need to use partial pressures.
You need to calculate the pressure at 47m, assume that you have O2 with a partial pressure of 1 atm. This allows you to calculate the partial pressure of He. From this you can work out the ratio of O2 to He by weight.

I think that you missed out how many molecules strike the wall in 1.6s. You can work out the kinetic energy for one molecule, the total energy of all the molecules striking the wall every sec and from there the pressure on the wall.

Answer 2

Somewhere in the class they must have given you a formula for how oxygen diffuses through the lungs membranes with amount and pressure of oxygen as variables. You need to use that to find the value for the amount of oxygen at 47m pressure that will give you the same result for absorbed oxygen as the normal amount of O2 at 1atm gives you.
The second give me a headache. Sorry.