A soccer player kicks a ball from the ground level at an angle of 60.0° with an initial speed of 20.0 m/s towards the goal. Ignore air resistance. Assuming the goal is 50.0 m away from the player, and the goalkeeper starts moving towards the ball from the goal line at the instant the ball is kicked, with a constant speed to catch the ball just before it lands. Find the speed at which the goalkeeper must move.