A uniform tube with an open stopcock is lowered into mercury so that 15 cm of the tube remains unfilled. The stopcock is closed and the tube is lifted by 10 cm. Find the height y of mercury in the tub

Question

A uniform tube with an open stopcock is lowered into mercury so that 15 cm of the tube remains unfilled. The stopcock is closed and the tube is lifted by 10 cm. Find the height y of mercury in the tube above the outer level (cm, nearest 0.1). Atmospheric pressure is 76 cm of Hg.

TestHub · Accepted Answer

The trapped air is 15 cm at 76 cm of Hg. After the lift its length is 25 − y and its pressure is 76 − y . So ( 76 − y ) ( 25 − y ) = 76 × 15 , giving y 2 − 101 y + 760 = 0 and y = 8.2 cm.

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