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In a siphon, the reservoir's surface area is far larger than the uniform tube's cross-section. The lower (outlet) end of the tube is 6 m below the water surface. Taking water density = 10³ kg/m³ and atmospheric pressure = 10⁵ N/m², what is the maximum height H (measured above the water surface) of the highest point of the siphon for it to keep working?

1. 1 m
2. 6 m
3. 10 m
4. 16 m

Correct answer: 10 m

Solution

A siphon works as long as the pressure at its highest point stays positive. The greatest height of the crest above the reservoir surface that atmospheric pressure can sustain is H = P_atm/(rho*g) = 10⁵/(10³ * 10) = 10 m.

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