features of a harmonic motion

Question

Fig shows a mass attached to two springs. The mass moves along a horizontal tube with one spring stretched and the other compressed. A narrow marked on the mass indicates its position on a scale. fig1 shows the situation when mass is displaced through a distance x from its equilibrium position.The mass is experiencing an acceleration a in the direction shown. fig2 shows a graph of the magnitude of the acceleration against the displacement x.

State one feature from each figure which shows that the mass per forms harmonic motion when released.

Fig-1

 Fig-2

Summary : features of a harmonic motion due to mass