Question

The manual of a truck instructs the driver to inflate the tyres to pressure $210kPa$. What is the recommended absolute pressure? 1 atmospheric pressure = 101kPa.
A. $210kPa$
B. $311kPa$
C. $109kPa$
D. $20kPa$

Answer 1

The amount of pressure measured by any instrument is referred to as to be the gauge pressure. It is relative to the atmospheric pressure. The amount of pressure above or below a reference pressure (atmospheric pressure) is termed as gauge pressure. Its value depends on the absolute pressure.
As per the given data,
The air pressure in the tires (Gauge pressure) is $210kPa$
Atmospheric pressure is $101kPa$

Formula used:
$P-{{P}_{a}}={{P}_{G}}$

Complete step-by-step answer:
The gauge pressure can be calculated by Open Tube Manometer. It is a U-shaped tube partially filled with mercury (Hg). One end is open and the other is connected to some device to determine the pressure. Gauge pressure is the sum of the absolute pressure and the atmospheric pressure around the body. Mathematically,
$P-{{P}_{a}}={{P}_{G}}$
By rearranging we can say that the absolute pressure will be,
$P={{P}_{G}}+{{P}_{a}}$
Absolute pressure is the sum of the gauge pressure and the atmospheric pressure. It is measured relative to a full vacuum above the absolute zero pressure.
By putting the values as there the given data,
$\begin{aligned} & P=210kPa+101kPa \\\ & \Rightarrow P=311kPa \\\ \end{aligned}$
It can be measured using a setup named barometer.
So the recommended absolute pressure is $311kPa$. And the correct option for the question is Option B.

So, the correct answer is “Option B”.

Note: A tyres or tire is a ring-shaped component that surrounds a wheel’s rim. It helps to transfer a vehicle’s load from the axle through the wheel to the ground and it is also used to produce a moving force over the surface of the wheels. They have straps in them so that they can produce a frictional force also for the motion of the body.