Question

A barometer kept in an elevator accelerating upward reads 76 cm. The air pressure in the elevator is
(a) 76 cm
(b) < 76 cm
(c) > 76 cm
(d) zero

Answer 1

A barometer kept in an elevator accelerating upward reads 76 cm. The air pressure in the elevator is greater than 76 cm.

Explanation:

When a barometer kept in an elevator accelerating upward 76 cm, the pseudo force to downward direction will be increased and then the net acceleration will be sum of a and g.

i.e. a’=(g+a)

Pressure = hρ(g+a)

               $=76+\mathrm{a} / \mathrm{g}(\text {which } \mathrm{is}>76\,{cm} \text { of } \mathrm{Hg})$

In other words, we all know that pressure P = (force/area) which mean force is directly proportional to pressure. So, the air pressure in the elevator is greater than 76 cm.