# Actual tyre pressure

## Homework Statement

On a warm day, a student uses a tire gauge to test the air pressure of her tires. While listening to the weather report on the way to the garage, she finds that the barometric pressure is 780mmHg. If the gauge reads a pressure of 35psi, what is the actual pressure inside the tires in psi?

## Homework Equations

I don't know which equation I should be using. Is it a trick question because the tyre pressure doesn't change or is it
Pgauage= Pabsolute - Pambient

## The Attempt at a Solution

if it is then I'm assuming that absolute pressure is the same as actual pressure.
Then
Pgauage= 35psi
Pambient= 780mmHg= 15.0868psi
and I have to find Pa
which would be
Pabsolute=35 + 15.0868
= 50.868 psi

Like I said I have no idea....thanks!

## Answers and Replies

ehild
Homework Helper
Pgauage= 35psi
Pambient= 780mmHg= 15.0868psi
and I have to find Pa
which would be
Pabsolute=35 + 15.0868
= 50.868 psi

It looks all right, but the end result. Check the addition! ehild