CBSE Class 9 Physics, Work and Energy

•   Work done on an object is defined as the magnitude of the force multiplied by the distance moved by the object in the direction of the applied force.

      Work done = force × distance

                                    = F × s

      1 Joule = 1 Newton × 1 metre.

      The unit of work is joule.

•   Work done by a force acting obliquely is equal to W = F cos θ × s

•   Work done on a body moving in circular path is zero.

•   The energy of a body is its capacity of doing work. The S. I. unit of energy is Joule (1 KJ = 1000 J).

•   Form of energy : (P.E & K.E.), heat energy, light energy, sound energy etc.

•   Kinetic energy is the energy possessed by a moving body by virtue of its motion.

•   Kinetic energy

•   Potential energy is the energy possessed by the body due to its position or shape.

•   Potential energy = mgh

•   Law of conservation of energy states that whenever energy gets transformed from one form to another, the total energy remains unchanged. i.e., energy can neither be created nor destroyed.

•   Power is defined as the rate of doing work. S.I. unit of power is Watt. (W).

•   Commercial unit of energy is kWh (kilowatt –hour).