A ball is held between two fixed points A and B by means of two stretched springs, as shown in the figure below.
The ball is free to oscillate along the straight line AB. The springs remain stretched and the motion of the ball is simple harmonic. The variation with time 
of the displacement 
of the ball from its equilibrium position is shown in the graph below.
Calculate the displacement of the ball at which its kinetic energy is equal to one-half of the maximum kinetic energy.
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