Density (Cambridge O Level Physics)

A student is determining the density of wood by two methods.

He is using the wooden rod shown in Fig. 1.1.

Method 1

The dimensions of the wooden rod are shown full size in Fig. 1.2.

The student uses a balance to measure the mass m of the wooden rod as shown in Fig. 1.3.

Record the mass m of the rod.

m = ............................................................g

Calculate a value ρ₁ for the density of the wooden rod. Use the values l = 4.5 cm and d = 2.0 cm, the value of the mass, and the equation . Include a suitable unit.

ρ₁ = ........................................................

Method 2

The student pours water into a measuring cylinder as shown in Fig. 1.4.
He then floats the wooden rod in the water as shown in Fig. 1.5.

Record the reading V₁ of the water level in the measuring cylinder as shown in Fig. 1.4.

V₁ = ........................................................cm³

Record the new reading V₂ of the water level in the measuring cylinder with the rod floating in the water as shown in Fig. 1.5.

V₂ = ........................................................cm³

[1]

The student removes the rod and lowers a piece of modelling clay into the water as shown in Fig. 1.6.

He then hooks the rod to the modelling clay and lowers them into the water as shown in Fig. 1.7.

He records the new reading V₃ of the water level in the measuring cylinder with the modelling clay.

He records the reading V₄ of the water level in the measuring cylinder with the modelling clay and rod.

V₃ = 164 cm³

V₄ = 178 cm³

Calculate another value ρ₂ for the density of the wooden rod. Use the values from (c) and (d) and the equation  where k = 1.0 g/cm³.

ρ₂ = ........................................................

On Fig. 1.8, draw an arrow showing the correct line of sight for reading the volume of water in the measuring cylinder.

Suggest a possible source of inaccuracy in Method 2, even if it was carried out carefully.