☰
Work, Energy and Power
The absolute value of potential energy and therefore total energy has no physical significance. It is the difference of potential energies that matters. One can, therefore, add or subtract a constant to the potential energy provided we do it to potential energy at every position for a given force without any change in the physical situation. By convention, for forces which fall off to zero at large distances, the potential energy at infinity is taken to be zero. With this choice, is the potential energy positive or negative for,
(a) electron-position bound state,
(b) planet-satellite system,
(c) electron-electron system?
(a) Because e–, e+ pair attracts each other due to electrostatic force, and if potential energy at infinity is taken to be zero, then an electron-positron pair in the bound state will have negative potential energy.
(b) The planet-satellite system attracts each other due to gravitational force. Therefore, the system has negative energy.
(c) Electron-electron repels each other, therefore to bring them close to each other, energy is required which is stored in the form of potential energy. Therefore, the potential energy of system becomes positive.
Sponsor Area
By eating two apples, a person starts pushing the wall of room. If food value of apple is 100 calories per apple, how much work he will do in pushing the wall in one hour?
Sponsor Area
Sponsor Area