Question

# A barometer kept in an elevator reads 76 cm when the elevator is accelerating upwards. The most likely pressure inside the elevator (in cm of Hg) is A. $74$B. $75$C. $76$D. $77$

Hint: When the elevator is going upwards with acceleration a then net acceleration will be the sum of a and g. A barometer is a scientific instrument used to measure atmospheric pressure, also called barometric pressure.
i.e. $a+g$

Formula used:
Pressure = $h\rho \left( g+a \right)dyne/c{{m}^{2}}$
$\rho$= density of material

As given in problem that barometer is going upwards with elevator so,
Pressure = $h\rho \left( g+a \right)dyne/c{{m}^{2}}$
\begin{align} & P=76\times 13.6\times \left( g+a \right) \\ & p=76\times 13.6\times g \\ \end{align}
$1+\dfrac{a}{g} > 1 cm Hg$
So, the final pressure for this will be more than $76cm$ of Hg.

Hence the correct option for this is option (D).

Barometers and pressure altimeters (the most elementary and customary sort of altimeter) are essentially an equivalent instrument, but used for various purposes. An altimeter is meant to be used at different levels matching the corresponding air pressure to the altitude, while a barometer is kept at an equivalent level and measures subtle pressure changes caused by weather and elements of weather. The average atmospheric pressure on the earth's surface varies between $940$ and $1040hPa\left( mbar \right)$. The average atmospheric pressure at sea level is $1013hPa\left( mbar \right)$