Work Energy and Power Revision Notes for NEET Physics PDF Download
⚡ WORK, ENERGY & POWER · WEP
Work-energy theorem • Kinetic & Potential energy • Conservation of mechanical energy • Power • NEET problems
📐 WORK (W)
Work done by constant force: W = F·s = F s cosθ (scalar product)
Special cases:
θ = 0° → W = Fs (maximum positive)
θ = 90° → W = 0 (no work)
θ = 180° → W = –Fs (negative work)
Work by variable force: W = ∫ F·dx (area under F-x graph)
📊 Work as area under F-x curve
🔋 ENERGY & WORK-ENERGY THEOREM
Kinetic Energy (KE): K = ½ mv²
Potential Energy (PE): U = mgh (gravitational), U = ½ kx² (spring)
Work-Energy Theorem: Wnet = ΔK = Kf – Ki
🔄 CONSERVATION OF MECHANICAL ENERGY
When only conservative forces act: Etotal = KE + PE = constant
🎢 Example: Free fall
mgh + ½ mv² = constant. At height h, v = √(2g(H–h)).
🔧 Spring-mass system
½ mv² + ½ kx² = ½ kA² (amplitude A).
✏️ Energy conversion in pendulum
PE ⇄ KE
⚡ POWER (P)
Average power: Pavg = W/Δt
Instantaneous power: P = dW/dt = F·v (dot product)
Unit: Watt (W) = J/s. 1 hp = 746 W
Efficiency: η = (output power)/(input power) × 100%
💡 NEET TIPS & SHORTCUTS
- Work done by gravity is independent of path: Wg = –ΔU = –mgΔh.
- Work done by spring force: Wspring = –½ k(x₂² – x₁²).
- For variable force, use integration or area under F-x.
- In collisions, kinetic energy may not be conserved, but momentum always is.
⚠️ COMMON MISTAKES
- Confusing work done by friction with change in kinetic energy (friction always does negative work).
- Using conservation of energy when non‑conservative forces are present.
- Not using the correct sign for work done by a force.
- Assuming power = force × speed always – only valid when force and velocity are in same direction.
📌 QUICK REVISION CARD
Work (constant force): W = Fs cosθ
Kinetic energy: K = ½ mv²
Gravitational PE: U = mgh
Spring PE: U = ½ kx²
Power: P = Fv (if F∥v)
Work-energy theorem: Wnet = ΔK