Deflating tire, thermodynamics problem

Melgibson
Messages
6
Reaction score
0

Homework Statement


Find the size of the hole in the tire after it has taken 60minutes to become flat.

Homework Equations


Impulse = F*Deltat = DeltaN*Deltap (N=molecules, p=momentum) , P = F/A (A is area of hole), Equipartition for gas in 1-d -> 1/2kT = 1/2mv^2
Derivative of ideal gas law (assuming T and V are constant) = dPV=dNkT

The Attempt at a Solution


the general equation i came up with that describes the decrease in pressure as a function of time is P = e^-((Aroot(kT)/(2Vroot(m)) *t) + P(initial)) actually ill upload a typed image
flkqyv.jpg


Using a known volume of a tire i am trying to find the initial pressure but I am having trouble figuring out how to do it any help would be appreciated. Also I am not sure if i have made a mistake in deriving this equation

Ummm have i explained well enough? Is there more i need to include? Or is the answer not simple? I am sort of waiting for an update if someone could clarify it would be nice.
 
Last edited:
Physics news on Phys.org
Oh i see where i made the mistake. After the integration there should be 1 constant on each side to be combined into another constant which is not P(initial). What a silly mistake. From there it is pretty straightforward.
 
To solve this, I first used the units to work out that a= m* a/m, i.e. t=z/λ. This would allow you to determine the time duration within an interval section by section and then add this to the previous ones to obtain the age of the respective layer. However, this would require a constant thickness per year for each interval. However, since this is most likely not the case, my next consideration was that the age must be the integral of a 1/λ(z) function, which I cannot model.
Back
Top