Work, Energy and Power

“Work, energy, and power are fundamental concepts that describe how forces interact with objects and how energy is transferred or transformed.”

What is Work?

Work is said to be done when a force is applied on an object and the object is displaced in the direction of force. Mathematically,

  • Work (W) = Force × Displacement × cosθ

Where θ is the angle between force and displacement. Work is a scalar quantity and its SI unit is Joule (J).

What is Energy?

Energy is the capacity to do work. It exists in different forms such as kinetic energy, potential energy, thermal energy, etc.

  • Kinetic Energy (KE) = ½ mv²
  • Potential Energy (PE) = mgh

Energy is also a scalar quantity. Its SI unit is Joule (J).

What is Power?

Power is the rate of doing work or the rate of transfer of energy. It tells how fast work is done.

  • Power (P) = Work / Time

The SI unit of power is Watt (W). 1 kilowatt (kW) = 1000 watts. The commercial unit of energy is kilowatt-hour (kWh).

Types of Work

  • Positive Work: When force and displacement are in the same direction.
  • Negative Work: When force and displacement are in opposite directions.
  • Zero Work: When displacement is zero or force is perpendicular to displacement.

Law of Conservation of Energy

Energy can neither be created nor destroyed; it can only be transformed from one form to another. The total energy of an isolated system remains constant.

Previous Year Questions

  • HSSC JE 2020: A 2 kg object is moving at a speed of 3 m/s. What is its kinetic energy?
  • KE = ½ × 2 × 3² = 9 J
  • RRB JE 2019: If 100 J of work is done in 10 seconds, what is the power?
  • P = 100 / 10 = 10 W
  • SSC CGL 2021: Which type of energy is stored in a stretched rubber band?
  • Potential Energy

Important Points

  • 1 Joule = 1 Newton × 1 meter
  • 1 kWh = 3.6 × 106 J
  • Kinetic energy is due to motion, potential energy is due to position.
Note: Machines are never 100% efficient due to energy losses like heat, sound, and friction.

Conclusion

Work, energy, and power are interrelated and essential to understanding motion and machines. These concepts help in analyzing mechanical systems and everyday phenomena.

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