A block of mass \(m\) is placed on a frictionless horizontal surface and attached to one end of an ideal spring with spring constant \(k\). The other end of the spring is fixed to a wall. The block is pulled to a displacement of magnitude \(A\) from its equilibrium position and released from rest, causing it to oscillate in simple harmonic motion. Which of the following is a correct expression for the speed of the block when it is at a position \(x = \dfrac{A}{2}\)?