Illustrate the law of conservation of energy by discussing the energy changes which occur when we draw a pendulum bob to one side nd llow it to oscillate. Why does the bob eventually come to rest? What happens to its energy eventually? Is it a voiltion of the law of conservation of energy?

The potential energy of a freely falling object decreases progressively. Does this violate the law of conservation of energy ? Why ?

The bob of a pendulum is released from a horizontal position. If the length of the pendulum is 1.5 m, what is the speed with which the bob arrives at the lowermost point, given that it dissipated 5% of its initial energy against air resistance ?

Two pendulums with identical bobs and lengths are suspended from a common support such that in rest position the two bobs are in contact. One of the bobs is eleased after being displaced by 10^@ so that it collides elastically head-on with the other bob. Draw a graph showing variation in energy of either pendulum with time, for 0le t le 2T , where T is theh period fo each pendulum.

Bohr's model of hydrogen atom In order to explain the stability of atom and its line spectra, Bohr gave a set of postulates: An electron in an atom revolves in certain circular orbit around the nucleus. These are the orbits for which mvr=(nh)/(2pi) In these allowed orbits, the electron does not radiate energy. When an electron jumps from higher energy level E_(n_2) to lower energy orbit E_(n_1) , radiation is emittd and frequency of emitted electron is given by v=(E_(n_2)-E_(n_1))/h . Further the radius of the n^(th) orbit of hydrogen atom is r=(n^2h^24piepsilon_0)/(4pi^2me^2) and energy of the n^(th) orbit is given by E_n=-13.6/n^2 eV . What would happen, if the electron in an atom is stationary?