Density, Upthrust & Viscous Drag (Edexcel A Level Physics)

Genuine crystal balls are made from clarified quartz rather than glass.

A student was given a small crystal ball and wanted to know whether it was genuine.

The mean diameter of the crystal ball was measured to be 5.06 cm and the mass of the crystal ball was measured to be 175 g.

Show that the density of the material of the crystal ball is about 2600 kg m⁻³.

The student measured the diameter of the crystal ball using vernier calipers with a resolution of 0.01 cm.

She measured the mass of the crystal ball using a balance with a resolution of 1 g.
 
The table gives the densities of clarified quartz and glass.

Determine whether the crystal ball was genuine.

A student investigated the terminal velocity of steel spheres falling through oil.

The student obtained the following results.

radius of steel sphere = 1.50 mm
volume of steel sphere = 1.41 × 10⁻⁸ m³
mass of steel sphere = 1.10 × 10⁻⁴ kg
maximum speed of sphere = 0.849 ms⁻¹

The student had the following table.

Identify which type of oil the student used.

The values in the table are for oil at 26°C.

Explain the effect of carrying out the investigation with oil at a lower temperature.