A cylindrical glass, closed at one end, of length 15 cm and cross-section 35 cm², is filled to a depth of 10 cm. A card is placed over the top and held there while the glass is inverted. What volume of water must leave the glass in order that the rest of the water should remain in the glass? Neglect the weight of the card.

Question

Quizplus · Accepted Answer

The pressure at the bottom of the glass must equal the atmospheric pressure for the water to remain in the glass when inverted. The volume of water that must leave is equal to the volume that creates a column of water 5 cm high (half the length of the air column, which is 15 cm - 10 cm of water = 5 cm), as the pressure at the bottom due to this column of water will then equal atmospheric pressure. The volume is calculated as the area of the cross-section (35 cm²) times the height of the column (5 cm), which equals 175 cm³ or 1.75 × 10⁻⁴ m³, rounded to two significant figures gives 1.74 × 10⁻⁴ m³.

A Cylindrical Glass, Closed at One End, of Length 15