Pressure and Depth
4 marks · NormalA reservoir contains a liquid with density . The reservoir is 15 m deep. Take .
Calculate the pressure difference between the surface and the bottom of the reservoir.
If a pipe runs from the bottom of the reservoir up to a point 7.5 m above the surface, what is the pressure difference between the bottom of the reservoir and the outlet of the pipe? Explain your reasoning.
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(a) 180000 Pa
(b) The pressure difference is due to a height of 22.5 m (from bottom to 7.5 m above surface); p = 22.5 x 1200 x 10 = 270,000 Pa. Pa
Common mistakes: not accounting for height above surface in (b)
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Marking points
M1 (a) · 1 mark · Substitutes correct values for h=15, ρ=1200, g=10.
A1 (a) · 1 mark · Correct final answer (180,000 Pa). (follow-through)
M2 (b) · 1 mark · States or identifies correct total height between bottom and pipe outlet (15+7.5 = 22.5 m), or explains height difference.
A2 (b) · 1 mark · Calculates correct value (270,000 Pa). (follow-through)
Worked solution
(a) Pressure difference:
(b) The outlet is 7.5 m above the surface, so total height from bottom to outlet is 15 + 7.5 = 22.5 m.