A block having the mass m and the charge +Q is connected to an insulating spring having a force constant k. The block lies on a frictionless, insulating, horizontal track, and the system is immersed in a uniform electric filed of magnitude E directed away from the spring. The block is released from rest when the spring is unstretched (at x=0). We wish to show that the ensuing motion of the block is simple harmonic. Call the initial configuration of the system that existing just as the block is released from rest. The final configuration is when the block momentarily comes to rest again. What is the value of x when the block comes to rest momentarily?