Q. 9

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 :

In a barometer accelerating upwards, the net acceleration is “g+a” where “a” is the upward acceleration of elevator. The pressure of an accelerating elevator and the one at rest is equal to atmospheric pressure. Hence, the heights will relate as




Where h’ is the height in the accelerating elevator, h is the height of mercury in an elevator at rest, 𝜌 is the density of the liquid.


So, the height in the accelerating elevator is less than that at rest.

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