# Gauge pressure and fluids problem

1. Jan 7, 2007

### kitty9035

1. The problem statement, all variables and given/known data[/b
An automobile tire having a temperature of .64 degrees C is filled to a gauge pressure of 27 lb ft/in2. What would be the gauge pressure in the tire when its temperature rises to 39 degrees C?
2. Relevant equations

Assume the volume remains constant, the air doesn't leak out, and the atmospheric pressure remains constant at 14.7 lb ft/in2

3. The attempt at a solution

i'm pretty sure your supposed to use the equation p=pg + po. How do I find the gauge pressure with a temperature increase??

2. Jan 7, 2007

### LeonhardEuler

You're right that you have to use that equation, and there is one other, too. What equation do you know that relates the pressure and temperature of a gas?

3. Jan 7, 2007

### kitty9035

would it be PV=nRT? I didn't learn about this yet. I just looked it up. What does the n and R stand for?

4. Jan 7, 2007

### LeonhardEuler

That's what I had in mind. If you haven't learned that, maybe you have learned some form of it for the particular case where the volume and amount of gas are constant? Does this look familiar?:
$$\frac{P_1}{T_1}=\frac{P_2}{T_2}$$
In this equation P and T are the absolute temperature and pressure, and 1 and 2 refer to different times.

By the way, in the ideal gas law "n" is the number of moles of gas and "R" is the universal gas constant, which is just a constant value.

5. Jan 7, 2007

### kitty9035

Thank you!! I got the answer:rofl:

6. Jan 7, 2007

### turdferguson

Proportions are always more precise because they are independent of sig figs