IB Physics HL S2.3 Concluding and Evaluating Topic Practice

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

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

The students search literature values and find the viscosity of this liquid to be 0.24 , when expressed in SI base units.

Suggest a conclusion reached by the students.

A boat is moved from land to water by rolling it across a set of cylindrical airbags.

When fully inflated, an unloaded airbag has a diameter of 1.80 m and a length of 24.0 m . At a temperature of $15^{\circ} \mathrm{C}$, an airbag can hold 4200 mol of gas.

Identify an assumption used in this estimation.

The boat is then released to roll down across the airbags. When the boat loses contact with an airbag at the top of the slope, the airbag expands adiabatically.

A student investigates whether the Stefan-Boltzmann law, $L=4 \pi \sigma R^{2} T^{4}$, applies to stars.
L= luminosity of the star, in W
$\sigma=$ Stefan-Boltzmann constant
R= radius of the star, in m
T= surface temperature of the star, in K
To verify the law, they obtain values from databases and manipulate the data as shown.

Outline a conclusion for the investigation.