WASSCE Physics · Paper 1 style

Properties of matter

One sample question with the full working. 23 more in the app, with instant feedback and repair sessions for the traps below.

A solid of mass 540 g has a volume of 200 cm³. Calculate its density in kg m⁻³.

A2700 kg m⁻³
B2.7 kg m⁻³
C370 kg m⁻³
D108 kg m⁻³

Show the answer and working

Answer: A

ρ = m/V = 540/200 = 2.7 g cm⁻³ = 2700 kg m⁻³ (1 g cm⁻³ = 1000 kg m⁻³).

Trap B Fails to convert units to SI: Convert every quantity to SI (m, kg, s) BEFORE substituting. 1 km/h = 1000/3600 m/s; 1 g = 10⁻³ kg; 1 cm² = 10⁻⁴ m².

Trap C Inverts a formula: Write the defining equation in words first (density = mass per unit volume), then rearrange algebraically. Check units: kg/m³.

Trap D Inverts a formula: Write the defining equation in words first (density = mass per unit volume), then rearrange algebraically. Check units: kg/m³.

Traps in Properties of matter

Fails to convert units to SI
Convert every quantity to SI (m, kg, s) BEFORE substituting. 1 km/h = 1000/3600 m/s; 1 g = 10⁻³ kg; 1 cm² = 10⁻⁴ m².
Inverts a formula
Write the defining equation in words first (density = mass per unit volume), then rearrange algebraically. Check units: kg/m³.
Confuses mass and weight
Weight is a force: W = mg (N). Mass (kg) is the amount of matter and does not change with g.
Rearranges a formula wrongly
Use the triangle or do the algebra: from V = IR, divide both sides by R → I = V/R. Check with units (V/Ω = A).
Upthrust and flotation errors
Archimedes: upthrust = weight of fluid displaced. A FLOATING body displaces its own weight of fluid. Relative density = weight in air ÷ loss of weight in water.
Calculates a different quantity
Name the quantity asked for and its unit before calculating. If your number has the unit of a different quantity, you used the wrong formula.
Reverses a relationship or direction
Write the relationship with an arrow or proportionality sign first (E ∝ f; R ∝ L; cooling a metal → R falls). Then check the option follows the same direction.
Uses everyday intuition instead of physics
Name the law that applies (Newton's first law, Archimedes' principle, kinetic theory) and reason from it. If the option only 'feels' right, test it against the law.
Treats inverse relations as direct
At constant temperature PV = constant: halving the volume DOUBLES the pressure. Charles: V/T constant with T in KELVIN.
Mixes up a pair of similar physics terms
Make a two-column table for each pair with one defining feature and an example. Underline the defining word in the stem before you look at the options.
Picks a related law, device or effect with a different job
Learn laws and devices as 'name → what it tells you' cards. Contrast neighbours: left-hand rule = motor force, right-hand rule = dynamo current, grip rule = field around a wire.
Friction and viscosity misconceptions
Limiting friction ∝ normal reaction (F = μR), independent of contact area. Static friction > kinetic. Friction can be useful (walking, brakes). Viscosity is fluid friction; terminal velocity reached when drag + upthrust = weight.

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