Power

Power is a quantity which tells how fast the work is done. Power is defined as the time rate of doing work i.e., the amount of work done in unit time.

Power = work done / time taken

SI Unit of power is watt. One watt is the power spent when 1 J work is done in 1 s. It is also measured in horse power.

1 horse power (H.P.) = 746 watts.

Daily Life Examples

  • About 1 J of work is done when you take a glass of water (200 mL) from your dinning table to your lips - a distance of about half metre.
  • A football player spends about 150 J of energy when he or she kicks a ball of about 1/2 kg to a height of 3 m.
  • A normal adult weighing about 50 kg does about 5000 J of work in ascending up the staircase of a single storey building.
  • In pulling out a 20 litre bucket of water from a 20 m deep well approximately 4000 J of work is done.