Dynamics

Work-Energy Principle

The work done on a body between two positions equals its change in kinetic energy.

The work-energy principle states T₁ + U₁₂ = T₂: the kinetic energy at the start plus the work done by all forces equals the kinetic energy at the end. Gravity does work equal to weight times the drop in height, a spring ½k(x₁² − x₂²), and kinetic friction always removes energy, μₖN times the distance slid.

It is the fastest route whenever a question gives two positions and asks for a speed, because it never needs the acceleration or the time. Kinetic energy uses mass, W/g in slugs in US units — using the weight directly is the most common error.

How much of the FE Civil exam is Dynamics?