  We investigate different types of collective excitations in a quantum dot
containing finite number of electrons at zero magnetic field. To estimate the
excitation energies analytically we follow the energy weighted sum-rule
approach. We consider the most general multipole excitation with angular
momentum l, and the breathing mode excitation (monopole excitation) of a large
quantum dot, for three different types of effective electron-electron
interaction. These are the logarithmic interaction, the short range
pseudopotential and the coulomb interaction. The ground state density of the
many-body system is calculated within Thomas-Fermi approximation. The
analytical results for the collective excitation energies and their dependence
on the system size and other external parameters are discussed in detail.
