1. The problem statement, all variables and given/known data Starting from rest, a child throws a ball of mass m with an initial speed v , at an angle B with the horizontal direction. The child then chases after the ball, accelerating at a constant acceleration a . If the child wants to catch the ball at the same height as it was thrown, what must be the child's acceleration a ? Express your answer in terms of some or all of the variables v , m , B and g for the gravitational constant. Express the trigonometric functions in terms of the basic sin(B), cos(B) or tan(B). 2. Relevant equations 1-D Kinematics 3. The attempt at a solution I'm using the point of release as the origin, positive-y is up and positive-x is the direction of the throw. I'm interested in the situation where at time t_f, x_child(t) = x_ball(t) and y_ball(t)=0. I start with the vertical. t_f is the moment of the catch v_yi is the initial vertical component of the ball's velocity; v_xi is the initial horizontal component of the ball's velocity y(t)=v_yi*t-1/2*g*t^2 t_f=2*v_yi/g For the horizontal component: x_ball = v_xi*t x_child = 1/2*a*t^2 At t_f: v_xi*t_f=1/2*a*t_f^2 Substituting gives: a=g*v_xi/v_yi With vector decomposition I get an answer of: a = g*v*cos(B)/sin(B) What am I doing wrong here?