The man pulls the boy up to the tree limb C by walking backward. If he starts from rest when {x}_{A} = 0 and moves backward with a constant acceleration {a}_{A} = 0.2 m/{s}^{2} , determine the speed of the boy at the instant {y}_{B} = 4 m . Neglect the size of the limb. When {x}_{A} = 0 , {y}_{B} = 8 m ,so that A and B are coincident, i.e., the rope is 16 m long .