(2) When playing the flute, the air column vibrates to make a sound. When the length of the air column is controlled differently, the vibration speed of the air column is different, so it will emit different tones;
(3)∫v = ST,
∴ sound propagation time t = SV = 680m340m/s = 2s;
So, the answer is: different; Tone; 2;