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Work and Energy – Summary

Physics, Work and Energy / By

Latest CBSE syllabus topics –
Work, Energy and Power – Work done by a force, energy, power. Kinetic and Potential energy, Law of conservation of energy.
Latest Maharashtra SSC Board syllabus topics –
Work, Energy and Power – Work done by a force, energy, power. Kinetic and Potential energy, Law of conservation of energy.

Summary –

  • Work is said to be done if a force is applied on an object and the object is displaced from its original position in the direction of the force.
    Work done (W) = Force (f) x Displacement (s)
  • Work can be positive, negative or zero, depending on the direction of displacement of the body. The SI unit of work is joule.
    1 joule = 1 newton x 1 metre.
  • Energy –  It is the capacity of a physical system to perform work. Energy exists in several forms such as heat, kinetic or mechanical energy, light, potential energy, electrical, or other forms. The SI unit of energy is the joule (J), same as that of work.
  • Mechanical energy is of two types-
    (a) Potential energy
    (b) Kinetic energy
  • Potential energy  – It is the energy possessed by a body due to its position or configuration.

    Potential energy of any object placed above ground (Ep) = mgh

  • Kinetic energy – It is the energy possessed by a body because of its motion.
    Kinetic energy  (Ek) = 1/2 mv2
  • Energy conversion – One form of energy can be changed into another form.
  • Law of conservation of energy – Energy can neither be created nor destroyed. It can be changed from one form to another.

Potential energy (mgh) + Kinetic energy (1/2 mv2) = Constant

  • The total energy of a system/ universe remains constant, though energy may transform into another form. Two billiard balls colliding, for example, may come to rest, with the resulting energy becoming sound and perhaps a bit of heat at the point of collision.
  • Power – Power is the time rate at which work is done or energy is transferred.

    Power (P) = Work (W) / Time (t) or Power (P) = Force (F) x Velocity (V)

  • The SI unit of power is the watt (W) or joule per second (J/s). 1 watt is the power of an agent, which does work at the rate of 1 joule per second.
  • Horsepower is a unit of power in the British system of measurement.

1 Horsepower = 746 Watt

  • Commercial unit of power is kilowatt hour (kWh).
    1kWh = 1000 W x 3600 s = 3.6 x 106J