The housing of the electric motor is freely pivoted about the horizontal $x$ -axis, which passes through the mass center $G$ of the rotor. If the motor is turning at the constant rate $\dot{\phi}=p,$ determine the angular acceleration $\ddot{\psi}$ which will result from the application of the moment $M$ about the vertical shaft if $\dot{\gamma}=\dot{\psi}=0 .$ The mass of the frame and housing is considered negligible compared with the mass $m$ of the rotor. The radius of gyration of the rotor about the $z$ -axis is $k_{z}$ and that about the $x$ -axis is $k_{x}$