Topic 7 of 8 · Form 5

Mechanics

Weight, normal contact force, tension, friction (F ≤ μR, limiting friction F = μR); resolving forces; equilibrium of a particle.

Notes for this topic 1 file, in order

Weight, normal contact force, tension, friction (F ≤ μR, limiting friction F = μR); resolving forces; equilibrium of a particle.

Constant acceleration equations; displacement–time and velocity–time graphs; variable acceleration using calculus (v = ds/dt, a = dv/dt).

F = ma for single particles and connected particles (pulleys, towing); motion on inclined planes.

Worked example: A 4 kg block on a rough slope at 30° (μ = 0.2) is released from rest. Find its acceleration (g = 10).

R = 40 cos 30° = 34.64; F = 6.93; 40 sin 30° − 6.93 = 4a → a = 3.27 m s⁻²

Conservation of momentum in direct collisions (including coalescence).

Work done = Fd cos θ; kinetic and potential energy; work–energy principle; power P = Fv; maximum speed when driving force equals resistance.

Exam tip: Use g = 10 m s⁻² in Cambridge 9709 mechanics unless told otherwise.

A 1 200 kg car's engine works at 24 kW against a resistance of 800 N. Find its maximum speed on a level road.
Find the work done by a 50 N force moving a box 6 m at 20° to the force.
A 2 kg particle at 5 m s⁻¹ collides with and sticks to a 3 kg particle at rest. Find the common speed.

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