A-LevelPhysicsForces, density and pressure9702/12 · Oct/Nov 2017 · Q151 Mark

Air is trapped inside a glass bulb which is immersed in water and attached to a U-tube containing mercury. The densities of water and mercury are ρw and ρm respectively. The surface of the water is open to the atmosphere where atmospheric pressure is P. [Figure showing a glass bulb with trapped air, immersed in water, connected to a U-tube with mercury, labelled with P, ρw, hw, ρm, hm] The acceleration of free fall is g. What is the pressure of the air in the glass bulb?

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AP + gρw hw + gρm hm

BP + gρw hw - gρm hm

Cgρw hw + gρm hm

Dgρw hw - gρm hm

✓ Correct answer

B: P + gρw hw - gρm hm

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Topic: Forces, density and pressure, A-Level Physics (syllabus 9702). Multiple choice, 1 mark.
Source: A-Level Physics, Oct/Nov 2017 Paper 1 Variant 2, question 15.

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