A seismic instrument is constructed so that m = 0.45 kg and c/c = 0.707. A spring with k = 2.9 kN/m is used so that the instrument will be relatively insensitive to low-frequency signals for displacement measurements and relatively insensitive to high-frequency measurements. Calculate the value of the linear acceleration that will produce a relative displacement of 2.5 mm while the frequency is 20Hz.