SSC CGL - Detailed Guide 2025
Self-Paced Course
Work, Energy, and Power
Reference: Lucent GK, NCERT Class 6–12
1. Work
Work is said to be done when a force is applied and there is displacement in the direction of force.
Work (W) = Force (F) × Displacement (d) × cosθ
(θ = angle between force and displacement)
| Type of Work | Condition | Example |
|---|---|---|
| Positive | θ < 90° (cosθ is +ve) | Lifting object upward |
| Negative | θ > 90° (cosθ is −ve) | Frictional force |
| Zero | θ = 90° (cosθ = 0) | Carrying bag horizontally |
- SI Unit: joule (J)
- 1 joule = 1 newton × 1 meter
- CGS unit: erg (1 J = 10⁷ erg)
- Work is a scalar quantity.
2. Energy
Capacity to do work.
| Type | Description | Formula / Example |
|---|---|---|
| Kinetic Energy (K.E.) | Energy due to motion | K.E. = ½mv² (m = mass, v = velocity) |
| Potential Energy (P.E.) | Energy due to position or configuration | P.E. = mgh (h = height, g = gravity) |
| Mechanical Energy | K.E. + P.E. | Total mechanical energy in system |
- SI Unit: joule (J)
- Energy is a scalar quantity.
- In absence of friction, mechanical energy is conserved (K.E. + P.E. = constant).
3. Work-Energy Theorem
- The work done by the net force on an object is equal to the change in its kinetic energy.
- This connects force, motion, and energy.
W = ΔK.E. = ½mv² − ½mu²
(Where u = initial velocity, v = final velocity)
4. Power
- Rate of doing work or rate of energy transferred.
- Power is a scalar quantity
Power (P) = Work done / Time = Energy / Time
| Quantity | Unit | Symbol |
|---|---|---|
| Power | Watt (W) | 1 W = 1 J/s |
| Bigger Units | Kilowatt (kW), Megawatt (MW) | 1 kW = 1000 W |
| Horsepower | 1 HP = 746 W | Used in engines |
5. Commercial Unit of Energy
- Commercial units are used in electricity bills:
- 1 kWh = 1 unit (used in electricity meter)
1 kilowatt hour (kWh) = 1000 W × 3600 s = 3.6 × 10⁶ J
Developed By Roopasree Challa
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