In the case of work (and also energy), the standard metric unit is the Joule (abbreviated J). One Joule is equivalent to one Newton of force causing a displacement of one meter. In other words, The Joule is the unit of work (if that helped any!)
If both containers are pushed with equal force, the one moving faster would have less mass
Image from a far away object formed by a concave mirror
I have no idea but this is my best guess as a sophomore in college
The change in pitch of a train's horn as it passes while you are
standing still can be described by the Doppler effect, but that
doesn't explain it.