# Homework Help: Pressure = F/A

1. Jun 28, 2007

### kiwikahuna

1. The problem statement, all variables and given/known data
Air within the funnel of a large tornado may have a pressure of only 0.2 atm. Atmospheric pressure is 101300 Pa. What is the approximate outward force F on a 11m X 16 m wall if a tornado suddenly envelopes the house? Answer in units of N.

2. Relevant equations
P = F/A

3. The attempt at a solution

I converted 0.2 atm to 20260 Pa. The area is 11m X 16 m = 176 m^2.

F = (20260 Pa) (176 m^2)
F = 3.56576 X 10^6 N

The answer is wrong. What did I overlook?

2. Jun 28, 2007

### ice109

is there 0 pressure inside the house?

3. Jun 28, 2007

### kiwikahuna

The problem doesn't say.

4. Jun 28, 2007

### Staff: Mentor

For one thing, you only calculated the inward force exerted by the air outside the house. As ice109 says, you forgot that it's the air inside the house that pushes the walls outward. (Find the net force.)

5. Jun 28, 2007

### ice109

you have to infer it. if this house is inside the atmosphere is there zero pressure inside the house?

6. Jun 28, 2007

cheater...