Question

Consider the equations

$P=\underset{\Delta S \rightarrow 0}{L i m}\frac{F}{\Delta S}$ and $P_{1}-P_{2}=\rho gz$

In an elevator accelerating upward,

• A. both the equations are valid
• B. first is valid but not the second
• C. second is valid but not the first
• D. both are invalid

Answer 1

Answer: (B)

Equation 1 is universal equation of pressure but the second equation is valid only when it is in state of rest, while moving upward the pressure difference is $\Delta P=z\rho \left(g + a\right)$