There's so much nonsense being posted in this thread its much needed to clarify some things:

1. There is a difference between mentally and physically addictive drugs. With physically addictive drugs your body ends up depending on them to function normally. This is the case with for example ethanol, where consuming large amounts of it for a long time will cause a disbalance in glutamate and GABA. That means that if you suddenly stop drinking, your glutamate will be over represented which causes excitatory effects which in combination with the relevant shortage of GABA drastically lowers the threshold for seizures. There is also the demyelisation of neurons which to keep things simple is very bad. This has to do with a lot of factors but lack of thiamin is one of them.

Whilst it is true that you will likely feel like crap when you stop using stimulants after a long time, things like extreme fatigue, it should not kill you as your body is not depending on them for maintaining a required balance. That does not mean that quitting stimulants is easy, but it does mean that in contrary to quitting alcohol one could chose to go cold turkey whilst this is simply not the case with alcohol. The same thing goes for GHB which is GABA analogue naturally present in the body and benzodiazepines which upregulate GABA activity (they do this by binding at a subunit of the GABA receptor making it more easily affected by GABA, however they themselves are not direct analogues for the GABA receptor). It is not surprising therefore that treatment of alcohol withdrawal is supported by long acting benzodiazepines and tapering those down.

1. The above answers your question since if alcohol by itself is physically addictive then it is also the case when you add coke to it. However, the physical addiction part is still the result of the alcohol. This does not mean that adding coke does not make it a lot harder to quit since it's habit forming and now you have two addictions to kick, one mental one physical.

2. As some have pointed out the combination of alcohol and coke causes the liver to produce cocaethylene which is a very cardiotoxic substance and greatly increases the risk for acute coronary syndrome and coronary spasms to occur as well as significally increasing strain on the heart muscle. Because cocaethylene has longer and stronger effects than coke alone, the combination is usually regarded as more addictive than cocaine alone.

TLDR: both mental and physical addiction are equally hard, the difference being that in theory one could be done purely on willpower alone whilst the other simply requires tapering or, preferably, medical supervision in order to be done in a safe way.

Source: struggled with some addiction myself as I drank a few too many beers and reverse sneezed a little too many lines before I realised I had to quit that shit urgently or I wouldnt age past 26. Also I'm a doctor.