5 Must-Know Facts — Work, Energy & Power — Summary

Work-Energy Theorem: W_net (ALL forces) = $\Delta K$ E. Always include friction. Never omit any force.
String vs Rod: String → v_top(min) = √(gR), v_bottom(min) = √(5gR). Rod → v_top(min) = 0, v_bottom(min) = √(4gR).
KE = $p^{2}$ /(2m): At equal momenta, lighter body carries more kinetic energy.
Collision rule: Momentum is ALWAYS conserved. KE is conserved ONLY in elastic collisions (e = 1).
Energy conservation caveat: KE + PE = constant ONLY when no non-conservative forces (friction, viscosity) act.