A vessel with square cross-section and height of 6 m is vertically partitioned. A small window of 100 cm2 with hinged door is fitted at a depth of 3 m in the partition wall. One part of the vessel is filled completely with water and the other side is filled with the liquid having density 1.5 103 kg/m3. What force one needs to apply on the hinged door so that it does not get opened? (Acceleration due to gravity = 10 m/s2)
Answer
150
Solution
Small window use the pressure at depth h = 3 m (atmospheric pressure cancels).
Water side: P1 = 1 gh = 103 10 3 = 3 104 Pa
Liquid side: P2 = 2 gh = 1.5 103 10 3 = 4.5 104 Pa
Net force: F = (P2 - P1)A = 1.5 104 100 10-4
F = 150 N (applied from the water side)
Answer: 150