ICSE Class 10 Physics: Work, Power & Energy — Full Notes 2026

Work Done by a Force

• W = Fs cos θ; when θ=90° work is zero (carrying a bag horizontally)
• Positive work (force and displacement same direction) vs. negative work
• Graphical interpretation: area under F–x graph = work done

Energy — Kinetic and Potential

• KE = ½mv²; derive from work-energy theorem
• GPE = mgh; elastic PE stored in compressed springs
• Mechanical energy = KE + PE; conservation in free fall

Work-Energy Theorem

• Net work done = change in kinetic energy: W_net = ΔKE
• Application: calculate speed after a net force acts over a distance
• Proof using Newton's second law and kinematics equations

Power

• P = W/t = Fv; SI unit Watt (W); commercial unit kilowatt-hour (kWh)
• Distinguish instantaneous vs. average power
• 1 horsepower = 746 W; conversion problems frequently asked

Simple Machines and Efficiency

• MA = Load/Effort; VR = dE/dL; η = MA/VR × 100%
• Why η < 100% always: friction and weight of movable parts
• Levers (class I, II, III) and pulley systems with VR calculations

Conservation of Energy — Applications

• Pendulum: PE at top ↔ KE at bottom; energy at any point
• Roller coaster problems using conservation of mechanical energy
• Energy transformations in daily life: electrical → light → heat

Numericals Practice

• Power of a pump lifting water: P = mgh/t
• A ball dropped from height h — find KE just before impact
• Efficiency of a crane: compare useful work to energy input