<p>The position, velocity and acceleration of a particle executing simple harmonic motion are found to have magnitudes of 4m, 2&nbsp;<span class="equation">\(ms^{-1}\)</span>&nbsp;and 16 <span class="equation">\(ms^{-2}\)</span>&nbsp;at a certain instant. The amplitude of the motion is <span class="equation">\(\sqrt{x}\)</span>​​​​​​​ m where x is_____​​​​​​​</p>