A particle in S.H.M. is described by the displacement function \[x(t)=a\cos (\omega t+\theta )\]. If the initial \[(t=0)\] position of the particle is 1 cm and its initial velocity is \[\pi \,cm/s\]. The angular frequency of the particle is \[\pi \,rad/s\], then it?s amplitude is [AMU (Med.) 2002]

• A.            1 cm                                         
• B.            \[\sqrt{2}\,cm\]
• C.            2 cm                                         
• D.            2.5 cm