# Pressure problems

1. Oct 10, 2004

### Deeviant

Ok I have the following question:

If the top of your head has a surface area of 113 cm2, what is the weight of the air above your head?

I'm not sure what I am doing wrong. I used the P = F/A. Solved for F to get F= P/A. I'm assuming the question is asking me for the force of the air on my head.

I'm using a figure of 1.013X10^5 Pa for atmospheric pressure, and I coverted cm to meters then divide the P(101300 Pa) by A(1.13) meters, and webassign told me to go fish.

I'm sure I'm doing something wrong, just not sure what.

2. Oct 10, 2004

### Sirus

Hmm. Try using kPa or keeping the area value in sq. cm. That might work.

3. Oct 10, 2004

### Deeviant

Hmm well I did make one stupid mistake when solving for F, F= P*A. Although I still can't seem it get it right. I'm sure its something to do with units, I have been having huge problems getting the units right lately, sometimes they just don't make sense.

It wants the answer in N. So I would assume I have to convert cm to m since N is in meters. But I'm just not having any luck today with this question, the silly thing is this is the first question and I have answer most of the harder ones already, just can't get this one.

4. Oct 10, 2004

### Deeviant

still need help..

5. Oct 11, 2004

### Leong

1 m = 100 cm
$$(1\ m)^2 = (100\ cm)^2$$
$$1\ m^2= 1X10^{4}\ cm^2$$
$$113\ cm^2= \frac{113}{10^4} = 0.0113\ m^2$$
$$F=P*A=1.013X10^5*0.0113=1145\ N$$