A railway tunnel is 660m long. An engineer standing at one entrance fires a starting pistol and listens for the echo from the far end.
(i) If the speed of sound in the air inside the tunnel is 340m/s, calculate the time after which the echo is heard.
(ii) Later that night the temperature falls, reducing the speed of sound in the tunnel air to 332m/s. Calculate the new time interval after which the engineer would hear the echo.