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Physics / Mechanics

Work, Energy and Power

Work refers to a process which involves a force and a resulting displacement in the direction of that force. Energy is nothing but the capacity of doing work. Power is nothing but rate of work done. The unit of work as well as enegy is 'joule' in SI system and 'erg' in CGS system. The unit of power in SI system is 'watt' and in CGS system is 'erg/sec'.

Work, Energy and Power Formulas

The formulas for Work, Energy and Power are given below,

Formula of Work

  • The work done by a force is calculated by multiplying the magnitude of force, the magnitude of displacement and the Cosine of the angle between the force and the displacement.

  • Work done, W = F*s*Cosθ, where 'F' is the force, 's' is the displacement, 'θ' is the angle between the force and the displacement.

Formula of Energy

  • Energy can exist in many forms, but all forms of energy can broadly be classified into either potential or kinetic energy. Potential energy is always relative depending on the reference that is chosen (generally height).

  • Potential Energy, P = mgh, where 'm' is the mass of the object, 'g' is the acceleration due to gravity and 'h' is the height at which the object is located.

  • Kinetic energy is the energy possessed by a body by virtue of being in motion.

    Kinetic Energy, K = 1/2*mv2, where 'm' is the mass of the object and 'v' is the velocity of the object.

  • The total mechanical energy of a body, which is the sum of potential and kinetic energies, remains constant when the body is in motion under the influence of a conservative force, which is nothing but a force that is used in moving a body from one place to another.

  • Law of conservation of energy states that energy can neither be created nor destroyed, and it can be transformed from one form to the other.

  • Work is the effort and Energy is the cause. Energy is intangible whereas work is tangible.

Formula of Power :

  • The power can be estimated by dividing work by time or enegy by time.

  • Power, P = W/t (or) E/t, where 'W' is the work done, 'E' is the enegy spent and 't' is the time during which the work is done or the enegy is spent.

  • If a body is able to spend more energy in a quicker time, it is said to be more powerful. For example, a 40 Watt bulb will consume 40 Joules of energy in every one second and a 60 Watt bulb will consume 60 Joules of enegy in every one second. Hence, 60 Watt bulb is considered more powerful.

  • In Electricity meters, 1 unit = 1KWh (KiloWattHour). That means a 1000 watt heater consumes 1 unit of energy if it is run for 1 hour. The unit of electricity consumption for which we pay our electric bill is the unit of energy, i.e. KWh is the unit of energy.