Work Energy And Power
- Work – when a force is applied to an object and object moves in direction of force.
Formula: Work = Force × Distance × cos(θ), Unit: Joules (J) - Energy – The capacity to do work. There are many forms (kinetic, potential, thermal, etc.).
Unit: Joules (J) - Power – The rate at which work is done or energy is transferred.
Formula: Power = Work / Time, Unit: Watts (W)
Work is said to be done when a force is applied on an object and the object is displaced in the direction of the force. If any of these is missing, no work is done (even if effort is made). Formula for Work,
- Work (W) = Force (F) × Displacement (s)
- Unit of Work = joule (J) (1 joule = 1 newton × 1 metre)
Example : 5 N force, 2 m displacement ➝ Work = 10 J
Energy is the capacity to do work. It is transferred from one object to another when work is done.
- Unit of energy = joule (J), and 1 kJ=1000 J.
- Energy exists in several forms: Mechanical Energy (potential + kinetic), heat, chemical, electrical, and light energy.
Kinetic Energy is the energy possessed by an object due to its motion. A moving object can do work based on its speed. The faster it moves, the more kinetic energy it has. The formula for kinetic energy is: KE = 1/2 * mv²
Example : a 15 kg object moving at 4 m/s has K.E. = 1/2×15×4²=120 J of kinetic energy.
The work-energy theorem relates work done to the change in kinetic energy. If an object accelerates from velocity to v, the work done is: W=1/2*m(v²−u²)
Example : the work needed to increase the speed of a 1500 kg car from 30 km/h to 60 km/h is calculated using kinetic energy difference, resulting in 156250 J.
James Prescott Joule was a British physicist known for his work in electricity, thermodynamics, and the mechanical equivalent of heat. The unit of energy and work, joule, is named in his honor.
Potential Energy is the energy possessed by an object due to its position or configuration. The formula for kinetic energy is: PE = mgh
Example : 15 kg luggage lifted 1.5 m ➝ Work = 𝑚 × 𝑔 × ℎ =15×9.8×1.5=220.5J
Law of Conservation of Energy – Energy can neither be created nor destroyed; it only changes from one form to another. This law states that the total energy before and after transformation remains the same.
Power is defined as the rate of doing work, Formula for Power,
- Power = Work done (W)/ Time Taken (t)
- Unit of Power: Watt (W) (1 watt=1 joule/second)
- Average Power (Total energy consumed/ Total time taken) is used when power varies over time.