# Please help me in this homewok

1. Dec 7, 2009

### Dr.Wasim

1. The problem statement, all variables and given/known data

A cube 10.0 cm on each edge contains air ( with equivalent molar mass 28.9 gm/mol ) at
atmospheric pressure and temperature 300K. Find (a) the mass of the gas, (b) its weight,
(c) the force it exerts on each face of the cube. (d) Comment on the underlying physical reason why such a small sample can exert such a great force.

( I know it is simple quastion but i want to sure from my answer )

please i need the answer today

best wishes for you

2. Dec 7, 2009

### Oddbio

You will need the ideal gas law:
PV=nRT

Then write down what you know and your unknowns and see where you can go from that?
R is a constant R = 8.314472 J/(K*mol)

your pressure is a known btw, it says it is at atmospheric pressure.

3. Dec 7, 2009

### Dr.Wasim

ok

i found mass from ideal law

then

weight = mg

ok ?

now force = P * A right ?

p = 1 atm = 1.013 * 10^5 N/m^2 . are u sure ?

then i found F

ok

i need comment please

4. Dec 7, 2009

### Oddbio

I don't understand where your getting this from.
You had the equation right
Force = Pressure * Area.
So just multiply the atmospheric pressure by the area of one face on the cube. which is 100cm^2.

5. Dec 7, 2009

### Dr.Wasim

p = 1 atm = 1.013 * 10^5 N/m^2 ( Paskal )

it is known for evret one

and we found force in ( Newten ) so we must convert atm to paskal

now i want the answer for

(d) Comment on the underlying physical reason why such a small sample can exert such a great force.

6. Dec 7, 2009

### denverdoc

re d) what is gas made up of? what is the average velocity of a gas molecule at 300K? How many are banging into the walls at any one instant? Thats the sort of thing I think is being sought in the answer.

7. Dec 7, 2009

### Dr.Wasim

i don' what you mean

now see

i found force and it is equal 1013 newten and it is a great force

we have small sample of gas that exert this force on each face of cube

the quastion now .... what is phyiscal reason for that ?

Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook