i am running FFmpeg on linux server (ubuntu 14.04) and i try to cut video using this code

Code:
 ffmpeg  -ss 2  -i Cars.mp4  -t 6898  -c copy  Cars.1.mp4
( i also try -to flag )

and i try to merge 2 audio tracks with this code :

Code:
 ffmpeg -i  2s.mp3  -i Cars.mp3  -filter_complex amerge  -q:a 4  Cars.1.mp3
but none of this works , the first code just copy the file and the second code just copy the first track , thanks for the help .