Question

A barometer kept in an elevator reads $76cm$ 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. $77$

Answer 1

Answer: (D)

$77$

When the elevator is going upwards with acceleration $a$ then net acceleration will be the sum of $a$ and $g$(acceleration due to gravity).$=g+a$

$\therefore$ Pressure$=h\rho (g+a)$dyne/${cm}^2$

$=\frac{76\times 13.6\times (g+a)}{76\times 13.6\times g}$cm of Hg.

$=1+\frac{a}{g}>1$cm of Hg.

$\text{final pressure should be more than 76cm of hg}$