Aiming to determine the radius of a 2.5 kg metal ball by investigating the properties of standing waves, a scientist hangs the ball vertically at one end of a string that passes over a light, frictionless pulley. The string's second end is attached to a rigid support, as shown in the figure. The horizontal section of the string vibrates in its second harmonic when the ball is hanging in the air. While it vibrates in its fourth harmonic, the ball is completely submerged in a liquid of density 1.1 g/cm³. The string oscillation frequency is the same before and after the ball is completely submerged in the liquid. Determine the radius of the ball.