Chapter 5 — Work, Energy and Power

Work, energy, and power are fundamental physics quantities where work represents force applied over displacement, kinetic energy is the energy of motion, and power is the rate of work done—all related through the work-energy theorem which states that work done equals change in kinetic energy.

Chapter 5 covers work, energy, and power in mechanics. Work is defined as W = F·d (force times displacement component), kinetic energy as K = (1/2)mv², and power as P = dW/dt. Conservative forces like gravity and springs enable mechanical energy conservation, where total energy E = K + V(x) remains constant. The work-energy theorem states that work equals change in kinetic energy. Non-conservative forces like friction dissipate energy. Collisions conserve momentum but not always kinetic energy; elastic collisions preserve both, while inelastic collisions lose kinetic energy to deformation.

1. 01Work is done by a force only when there is displacement in the direction of the force; W = (F cos θ)d = F·d
2. 02Kinetic energy K = (1/2)mv² is always positive and represents energy due to motion
3. 03Conservative forces (gravity, spring forces) depend only on initial and final positions; non-conservative forces (friction) depend on the path
4. 04Mechanical energy is conserved for conservative forces: E = K + V(x) = constant, where V is potential energy
5. 05Power is the time rate of doing work: P = dW/dt = F·v, measured in watts (1 W = 1 J/s)
6. 06In collisions, linear momentum is always conserved; kinetic energy conserves only in elastic collisions, not in inelastic ones