Work-Energy Theorem

The net work done on an object equals its change in kinetic energy — a powerful shortcut that avoids needing acceleration or time in many problems.

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Overview

W = F·d·cos(θ), where θ is the angle between the force and displacement. The work-energy theorem states W_net = ΔKE = KE_f - KE_i. A force perpendicular to displacement (θ=90°) does zero work, regardless of its magnitude.

Practice Quiz

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A ball rolls without friction down a hill, starting from rest at height h. Using energy conservation, its speed at the bottom is:

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