A particle moves along a straight line so that its acceleration satisfies a=−0.5x, where x (in meters) is its position and a (in meters per second squared) is its acceleration. The particle is released from rest at x=4 m and moves toward the origin. What is its speed when it reaches x=0 m?
(a) 4 m/s
(b) 2 m/s
(c) 0 m/s
(d) 22 m/s