We want to find the force needed to get the pressure indicated in the image. We will get that the force must be F = -10.92N
Remember that pressure is equal to the quotient between force and surface.
In the image, we can see that there is a pressure P equal to -5mmHg, and the pressure inside the lungs is -2 mmHg, then we need to add another -3mHg to get P.
So we must have:
F/S = -3mmHg
Where F is the force and S is the surface.
F/280 cm^2 = -3mmHg
F = (-3mmHg)*(280 cm^2)
And we know that:
1 mmHg = 0.013 N/cm^2
Then:
-3 mmHg = -3*( 0.013 N/cm^2) = -0.039 N/cm^2
(We do this change of units so we can work with newtons).
F = ( -0.039 N/cm^2)*(280 cm^2) = -10.92 N
This is the force needed, the fact that is negative means that the force is actually inwards (you could already know this when you saw that the pressure P was smaller than the -2mmHg already in the lungs).
If you want to learn more about pressure, you can read:
https://brainly.com/question/356585
