Question

A barometer kept in an elevator reads 76 cm when it is at rest. If the elevator goes up with increasing speed,the reading will be

(a) zero

(b) 76 cm

(c) < 76 cm

(d) > 76 cm.

Answer 1

The correct answer is(c) < 76 cm

EXPLANATION:  

The pressure of the atmosphere remains the same in both the conditions =ρg*(0.76). But in the upward accelerating elevator the pressure of the mercury column =ρ(g+a)h, since these two are equal so h = (0.76){g/(g+a)}; clearly h<0.76 m i.e. h<76 cm.