# Barometer reading in an elevator .

## Homework Statement

A barometer kept in an elevator reads 76cm when it is at rest. If the elevator goes up with increasing speed , the reading will (a).increase (b)decrease (c)remain constant (d) become zero......

## The Attempt at a Solution

Dont have any clue.....can anyone give me a start?

supratim1
Gold Member

consider the change in total acceleration. if it is a upwards, then net accn = g + a

Ya i know that is the g effective you are talking about.....But what to do......with that....Do i apply Bernoulli's theorem at the top of the of the mercury surface in the tube and at the surface open to atmosphere?

supratim1
Gold Member

just use rho(g-effective)h

Can you give me a better explanation.....?

the atmos pressure is hXrhoXg(effective). the measurement is h, like "the pressure is 76cm". now if g effective is greater than g actual, h would have a less value for same pressure, and vice-versa.

Hi bjd40@hotmail.com....
So you mean to say that the pressure at the surface of mercury in beaker is same (equal to atmospheric pressure which is constant close to the earth).....SInce it is also = h*rho*geff as geff has become 'g+a' ie increased the 'h' has to decrease......Is that it?