iGCSE Physics (0625) 2.2.1 Thermal expansion of solids, liquids and gases Paper 4 -Exam Style Questions- New Syllabus

Correct Answer: $930\text{ kg/m}^3$ (to 2 sig. figs) or $933\text{ kg/m}^3$

Detailed solution: Density is defined as mass per unit volume. Using the formula $\rho = \frac{m}{V}$, we substitute the given mass $m = 2800\text{ kg}$ and volume $V = 3.0\text{ m}^3$. Calculating $2800 / 3.0$ gives $933.33…$, which is rounded to $930\text{ kg/m}^3$ to match the significant figures of the input data.

Correct Answer: $1400\text{ N}$

Detailed solution: First, calculate the liquid pressure at depth $h = 1.1\text{ m}$ using $p = \rho gh = 933 \times 9.8 \times 1.1 \approx 10000\text{ Pa}$. Next, determine the area of the block’s top surface: $A = 0.45\text{ m} \times 0.30\text{ m} = 0.135\text{ m}^2$. Finally, find the force using $F = p \times A$, which gives $10000 \times 0.135 \approx 1350\text{ N}$ to $1400\text{ N}$ depending on rounding of intermediate values.

Correct Answer: To allow for thermal expansion and prevent buckling.

Detailed solution: When the temperature increases, the steel rails undergo thermal expansion. At a microscopic level, the particles gain kinetic energy and vibrate more vigorously, causing the average separation between particles to increase. The gaps provide space for this increase in length, preventing the tracks from bending or buckling under stress.

Correct Answer: Plastic is a poor conductor (good insulator) of heat.

Detailed solution: Plastic is a suitable material for the handle because it has a low thermal conductivity. This significantly reduces the rate at which thermal energy is transferred from the hot metal pan to the user’s hand. As a result, the handle remains at a safe temperature to touch even while the water inside the pan is boiling.