The position co-ordinates of a particle moving in a 3-D coordinate system is given by $\mathrm{x}=\mathrm{a} \cos \mathrm{\omega } \mathrm{t}; \mathrm{y}=\mathrm{a} \sin \mathrm{\omega } \mathrm{t}$ and $\mathrm{z}=\mathrm{a} \mathrm{\omega } \mathrm{t}$The speed of the particle is :