A satellite revolves round the earth. Air preassure inside the satellite is maintained at 76 cm of mercury. What will be the height of mercury column in a baromerter tube of 90 cm long placed in the satellite?

The barometer tube is initially fully filled and the open end is closed temporarily, dipped into the mercury reservoir and then opened in the liquid. On the earth's surface, the atmospheric pressure at the level of the free surface of the mercury is balanced by the weight of the mercury column in the barometer tube. In the satellite, the value of g is zero, that is the things there are weightless. So the weight of the mercury column (initially 1 m) is zero. It means the column has no pressure at the reservoir level to balance the outer pressure of 76 cm of mercury. Therefore the level of the mercury in the barometer tube will not fall and it will remain 1 m.