Question 1

Explain, using particle theory, why a gas fills the entire volume of its container while a liquid takes the shape of the container but keeps a fixed volume. Include a labelled particle diagram for each state.

Accepted Answer

In a GAS: particles are far apart, move rapidly and randomly, exert negligible attractive forces on each other. They spread to fill all available space — hence fill the container fully.
In a LIQUID: particles are close together with moderate attractive forces. They can slide past each other (flow) so the liquid conforms to the container shape. The volume is fixed because particles cannot easily escape the attraction of neighbours.
Diagram: Gas — particles spread throughout box; Liquid — particles close together, no fixed arrangement but with a flat surface at the top.

Question 2

A car of mass 1 200 kg accelerates from rest to 30 m/s in 12 seconds on a straight road.
(i) Calculate the acceleration of the car.
(ii) Calculate the resultant force acting on the car. State the formula used.
(iii) State Newton's First Law of Motion and give ONE everyday example.

Accepted Answer

(i) a = (v − u) / t = (30 − 0) / 12 = 2.5 m/s²
(ii) F = ma = 1 200 × 2.5 = 3 000 N
(iii) An object remains at rest or in uniform motion in a straight line unless acted upon by a resultant (unbalanced) force. Example: a book lying still on a table stays still because the normal reaction and gravity are balanced.

Question 3

Magnesium ribbon burns in oxygen to form magnesium oxide.
(i) Write the balanced chemical equation for this reaction.
(ii) Classify this as a combination, decomposition, displacement or double-displacement reaction.
(iii) Name TWO signs that indicate a chemical reaction has occurred in this experiment.

Accepted Answer

(i) 2Mg + O₂ → 2MgO
(ii) Combination (synthesis) reaction — two substances combine to form one product.
(iii) Bright white light / flame produced; white ash (MgO) forms (any two of: light, heat, new substance formed, colour change accepted).

Question 4

In pea plants, the allele for tall (T) is dominant over the allele for short (t).
(i) Write the genotype and phenotype of a homozygous tall plant.
(ii) Two heterozygous tall plants are crossed. Using a Punnett square, predict the ratio of tall to short offspring.
(iii) Define the terms 'dominant allele' and 'recessive allele'.

Accepted Answer

(i) Genotype: TT. Phenotype: tall.
(ii) Cross: Tt × Tt → TT : Tt : tt = 1:2:1. Phenotype ratio: 3 tall : 1 short.
(iii) Dominant allele: the allele that is expressed in the phenotype even when only one copy is present (heterozygous). Recessive allele: only expressed in the phenotype when two copies are present (homozygous recessive).

Science 2022