In response to the comment of Mustafa (2013 J. Phys. A: Math. Theor. 46 368001) we justify our stand of considering an extended Lagrange equation involving a non-conservative force term when the particle mass varies with position. As has been known for some time, such an extended form not only takes into account the principle of virtual work applied to D'Alembert's principle but yields precisely the form of Newton's equation expected for a particle possessing a position-dependent mass. © 2013 IOP Publishing Ltd.

Bijan Kumar Bagchi

Physics

(SoNS) School of Natural Sciences

S. Das

S. Ghosh

S. Poria

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