CCEA A Level Physics 1.1 Physical Quantities and 1.2 Scalars and Vectors Exam Questions

About CCEA A Level Physics 1.1 Physical Quantities and 1.2 Scalars and Vectors

These two sections open Unit AS 1: Forces, Energy and Electricity and set up the language used for the rest of the CCEA course. You need to treat every physical quantity as a magnitude with a unit, reduce units to SI base units, and handle prefixes and standard form without slips. You then learn to separate scalars from vectors, resolve a vector into perpendicular components and combine vectors to find a resultant. These skills come back in moments, projectiles, momentum and fields. Examiners like short questions on base units and homogeneity of equations, and resolving forces for an object in equilibrium on a slope or held by ropes.

What you need to know

• Physical quantities Every quantity has a numerical magnitude and a unit. The SI base quantities you need are mass (kg), length (m), time (s), current (A), temperature (K) and amount of substance (mol).
• Derived units Express derived units in base units, e.g. newton = kg m s-2, joule = kg m2 s-2, pascal = kg m-1 s-2. An equation must be homogeneous (same base units on both sides) to be correct, although homogeneity alone does not prove it is correct.
• Prefixes and standard form Learn pico (10^-12), nano (10^-9), micro (10^-6), milli (10^-3), kilo (10^3), mega (10^6), giga (10^9) and tera (10^12). Convert to base units before substituting, e.g. 0.50 mm = 5.0 x 10^-4 m.
• Scalars and vectors A scalar has magnitude only (mass, speed, distance, energy, time). A vector has magnitude and direction (displacement, velocity, acceleration, force, momentum).
• Resolving vectors A vector F at angle θ to the horizontal has components F cos θ (horizontal) and F sin θ (vertical). Choose axes that make the problem simplest, such as along and perpendicular to a slope.
• Resultants and equilibrium Add perpendicular vectors using Pythagoras and find the direction with tan. For coplanar forces in equilibrium the resultant is zero, so the components in any two perpendicular directions each sum to zero, and three forces form a closed triangle.

Common mistakes in 1.1 Physical Quantities and 1.2 Scalars and Vectors

• Writing the unit of force as kg m s-1 instead of kg m s-2; always derive from F = ma.
• Forgetting to convert prefixes, e.g. using 5 mm as 5 m; convert to base units before substituting into any equation.
• Mixing up sin and cos when resolving; the component adjacent to the angle always uses cos.
• Calling speed or distance a vector; only quantities that need a direction to be fully described are vectors.
• Giving the size of a resultant but not its direction; a vector answer needs both, usually as an angle to a stated reference line.

Try three 1.1 Physical Quantities and 1.2 Scalars and Vectors exam-style questions