IB Physics HL A.2.11 Buoyancy and fluid equilibrium Question Bank

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

Exam points

Use Archimedes’ principle to calculate buoyancy in a fluid with known density and displaced volume.
Analyse how temperature or density changes alter floating fraction and equilibrium.
Evaluate a multi-force fluid model and justify which forces or approximations can be neglected.

[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.

All question bank results loaded

A.2.11—Buoyancy question 1