A tyre gauge reads 34 psi where atmospheric pressure is 14.7 psi. What is the absolute pressure inside the tyre?
A19.3 psi
B48.7 psi
C34.0 psi
D14.7 psi
Answer & Solution
Correct answer: B. 48.7 psi
1. Absolute pressure is gauge pressure plus atmospheric pressure.
2. The gauge reading of 34 psi is the gauge pressure, not the absolute pressure.
3. Absolute pressure = 34 psi + 14.7 psi = 48.7 psi, which is about 336 kPa.
4. The value 19.3 psi comes from subtracting instead of adding.
5. Quoting 34.0 psi treats the gauge reading as already absolute, which is the exact confusion the two terms exist to prevent.
_Source: OpenStax College Physics (CC BY 4.0), Ch 11 "Fluid Statics", section 11.6 Gauge Pressure, Absolute Pressure, and Pressure Measurement_
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