When the runner is halfway to first base, the triangle formed by his position and the first and second bases is a right triangle with legs of 45 ft and 90 ft. The angle between the runner's direction and the line from his position to 2nd base is ...
angle = arctan(90/45) ≈ 63.43°
The "speed made good" in the direction of 2nd base is the product of the cosine of this angle and the runner's speed toward first.