The manometer shown below is used to measure the difference in water level between the two tanks. Calculate this difference for the conditions indicated.

Options

A. 2 cm
B. 4 cm
C. 6 cm
D. 8 cm

Answer

B

Explanation

Using pressure equation from first to second tank surface
` p _ a + h _ 1 rho g - 40 rho _1 g + 40 rho g = p _ a + h _ 2 rho g `
` h _ 2 rho g - h _ 1 rho g = 40 rho g - 40 rho _ 1 g `
as ` rho _ 1 = 0.9 rho `
` (h _ 2 - h _ 1 ) rho g = 40 rho g - 36 rho g `
` h_ 2 - h _ 1 = 4 cm `