IB Physics HL A 2 11 Buoyancy Questions

Practise IB Physics HL A.2.11 by analysing buoyancy, density changes and equilibrium in complex floating or submerged systems.

Exam points

Explain buoyancy as the upward force from displaced fluid and apply Fb = ρVg with displaced volume.
Calculate buoyant force, density or displaced volume and use it in equilibrium or motion reasoning with complete evidence.

[Maximum number: 1]

A group of students is trying to determine the density and the viscosity of a liquid.

To determine the density, they use a balance to read the mass m of a sphere in air and immersed in the liquid.

They use a sphere of volume $V=1.827 \times 10^{-7} \mathrm{~m}^{3}$ .
The readings are $m_{\text {air }}=1.427 \mathrm{~g}$ in air and $m_{\text {immersed }}=1.208 \mathrm{~g}$ in the liquid.
The readings are different due to buoyancy. The buoyancy force $F_{\mathrm{b}}$ is given by

F_{\mathrm{b}}=\rho V g

where V is the volume of the sphere and $\rho$ is the density of the liquid.

Show that $F_{\mathrm{b}}$ is about 2 mN .

$(0.001427-0.001208) \cdot 9.8$ OR 2.1 mN

Allow the calculation to give a result
in mN or N . Look for full substitution
or answer with at least two SF.

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IB Physics HL A 2 11 Buoyancy Questions question 1