2016 · Q43
A Barometer kept in an elevator reads 760 mm when the elevator is at rest. When the elevator moves in the upward direction with increasing speed, the reading of the Barometer will be:
general-sciencephysics-mechanics
- A760 mm
- B> 760 mm
- C< 760 mm
- DZero
Explanation
In an elevator accelerating upward with acceleration a, the effective gravity becomes g + a (pseudo-force adds to weight). Since the barometric height h = P/(rho x g_eff), a larger effective g gives a shorter mercury column, so the reading falls below 760 mm. Note: the published key's page prints options (B) and (C) both as '< 760 mm' (a transcription typo), so there is no substantive dispute; the physics unambiguously gives less than 760 mm.