WORK, ENERGY, AND POWER

Diagram for principle of conservation of energy in a freely falling body.

Principle of Conservation.png

Frequently Tested Topics:

  • Conditions for work to be done and special cases

  • Conversions between units of work, power and energy

  • Derivation of expression of kinetic energy

  • Relationship between kinetic energy and momentum

  • Energy conversions from one form to another

  • Conservation of energy for a freely falling body and simple pendulum with diagrams (IMPORTANT)

*Note that other aspects of the chapter are equally important.

Important Past Questions:

  • State the energy changes in the given process. (2001, 2004, 2015)                                      Example: State the energy changes in the following while in use:                                                    i) burning of a candle                             ii) a steam engine

  • What should the angle between force and displacement be to get the i) minimum and ii) maximum work? (2005)

  • State and prove the principle of conservation of energy. [for a freely falling body/pendulum]            (2009, 2011, 2013)

  • Name the form of energy a body may possess even when it is not in motion. (2013)

  • Explain briefly why the work done by a fielder when he takes a catch in a cricket match is negative. (2015)

  • What is the work done by the moon when it revolves around the earth? (2014)

  • A man having a box on his head, climbs up a slope and another man having an identical box walks the same distance on a levelled road. Who does more work against the force of gravity and why? (2014)

  • A body is thrown vertically upwards. Its velocity keeps on decreasing. What happens to its kinetic energy as its velocity becomes zero? (2014)

  • A boy weighing 40 kgf climbs up a stair of 30 steps each 20cm high in 4 minutes and a girl weighing 30 kgf does the same in 3 minutes. Compare:

i) the work done by them​

ii) the power developed by them. (2016)

  • If the power of a motor be 100kW, at what speed can it raise a load of 50000N? (2017)

  • A body of mass 5 kg is moving with a velocity of 10 m/s. What will be the ratio of its initial and final kinetic energy, if the mass of the body is doubled and its velocity is halved? (2009) [IMPORTANT]

  • A ball of mass 0.20 kg is thrown vertically upwards with an initial velocity of 20 m/s/ Calculate the maximum potential energy it gains as it goes up. (2004)

  • The work done by the heart is 1 joule per beat. Calculate the power of the heart if it beats 72 times in one minute. (2005)

  • Two bodies of equal mass are kept at a height of 20m and 30m respectively, calculate the ratio of their potential energies. (2005)

  • A stone of mass 64g is thrown vertically upward from the ground with an initial speed of 20 m/s. The gravitational potential energy at the ground level is considered to be zero. Apply the principle of conservation of energy and calculate the potential energy at the maximum height attained by the stone. (g = 10 m/s^2)

Using the same principle, state what will be the total en​ergy of the body at its half way point? (2008)

List of All Important Formulae and Equations for Work, Energy, and Power