Cambridge IGCSE Physics 1 Motion, Forces and Energy Exam Questions

About Cambridge IGCSE Physics 1 Motion, Forces and Energy

Motion, forces and energy is the first and largest topic in the Cambridge IGCSE Physics 0625 syllabus. It runs from physical quantities and measurement techniques through motion graphs, mass and weight, density, the effects and turning effect of forces, centre of gravity, momentum, energy, work, power, energy resources and pressure. Extended candidates add more equations, including F = ma, momentum and impulse, kinetic and gravitational potential energy, and pressure in liquids. These ideas underpin thermal physics, electricity and space physics. Examiners expect confident use of equations with correct units, and regularly test speed-time graphs, the principle of moments and energy transfer calculations.

What you need to know

• 1.1 Measurement Use rulers, measuring cylinders and clocks or digital timers, and improve precision by measuring multiple values, e.g. timing several oscillations and dividing. Extended candidates distinguish scalars (speed, distance, mass, energy) from vectors (velocity, force, acceleration) and find a resultant of two perpendicular vectors.
• 1.2 Motion Speed = distance / time; acceleration = change in velocity / time. On a distance-time graph the gradient is speed; on a speed-time graph the gradient is acceleration and the area underneath is distance travelled. Acceleration of free fall near the Earth is about 9.8 m/s2.
• 1.3 and 1.4 Mass, weight and density Weight is the gravitational force on a mass: W = mg, with g = 9.8 N/kg. Density = mass / volume; measure the volume of an irregular solid by displacement. An object floats in a liquid if its density is lower than the liquid's.
• 1.5 Forces A resultant force changes speed, direction or shape. Load-extension graphs show the limit of proportionality; Extended candidates use F = ma and the spring constant k = F / x, and know that circular motion needs a force towards the centre. Friction and air resistance oppose motion and cause heating.
• 1.5 Moments and centre of gravity Moment = force x perpendicular distance from the pivot. For equilibrium there is no resultant force and no resultant moment: clockwise moments equal anticlockwise moments. Lowering the centre of gravity or widening the base increases stability.
• 1.6 Momentum (Supplement) Momentum p = mv. Impulse = FΔt = Δ(mv). Total momentum is conserved in collisions and explosions; resultant force = change in momentum / time.
• 1.7 Energy, work and power Energy stores include kinetic, gravitational potential, chemical, elastic, nuclear, electrostatic and internal (thermal). Work done = force x distance = energy transferred; power = work done / time. Efficiency = useful energy output / total energy input x 100%. Extended: Ek = 1/2 mv^2 and ΔEp = mgΔh. Compare renewable and non-renewable energy resources.
• 1.8 Pressure Pressure = force / area, measured in pascals (N/m2). Pressure in a liquid increases with depth and density; Extended candidates use Δp = ρgΔh.

Common mistakes in 1 Motion, Forces and Energy

• Confusing mass and weight. Mass is measured in kilograms and does not change; weight is a force in newtons and depends on g.
• Using the whole distance instead of the perpendicular distance from the pivot when calculating moments.
• Reading the area under a distance-time graph. Area under a speed-time graph gives distance; the gradient of a distance-time graph gives speed.
• Forgetting to square the speed in Ek = 1/2 mv^2, or squaring the half as well as the speed.
• Treating momentum as a scalar. Direction matters, so a velocity in the opposite direction must be given a negative sign.

Try three 1 Motion, Forces and Energy exam-style questions