A string 2.0 m long and fixed at its ends is driven by a 240 Hz vibrator. The string vibrates in its third harmonic mode. The speed of the wave and its fundamental frequency is :
(1) 320 m/s, 80 Hz
(2) 180 m/s, 120 Hz
(3) 320 m/s, 120 Hz
(4) 180 m/s, 80 Hz