State the differential equation of motion for an oscillator of mass m in the presence of a damping force directly proportional to the velocity.

Explanation

`m(d^2x)/(dt^2)+beta(dx)/(dt)+kx=0 " or " (d^2x)/(dt^2)+beta/m((dx)/(dt))+k/mx=0` is the required equation, where `beta` is the damping constant and k is the force constant of the motion.