Some words which mean "thinking over something deeply or for a long time "

I put together some words which generally means thinking over something deeply or for a long time. I know that we can not use every word in the same sentence just because they have similar meaning. So I would like to ask you to fill in my sentence with suitable words among them. Please choose more than one word if possible:

1. 
   

   I have been ................ my son (all day) since he left home for college.

   
   


2. 
   
   

   I have been ................ my debt. I owe $10,000, and I will have to pay it by next week, but I don't have enough money. So I have to find a way.

   
   


3. 
   

   I have been ................ my new school project. I don't know where to start.

   
   


4. 
   

   The government .............. how to stop the protests (about raising student fees).

   
   

My words:

• to ponder


• to mull over


• to contemplate


• to cogitate


• to deliberate


• to ruminate


• to dwell on

and any advice is welcome to help me discern the differences among them.

Answer

to ponder

means to, over a period of time, think about the consequences of two or more choices in a decision. If there is only one thing you are pondering, you are pondering whether or not to do that thing.

to mull over

is the same as ponder - but you can mull over collective nouns, meaning you are trying to decide which one of the group. "I mulled over the candy, and found a good piece."

to contemplate

means to think about the consequences of something carefully, thoroughly, and for a long time. Typically when you contemplate something, you are deciding whether or not to do it, not picking among an array of choices. It has a serious connotation, likely due to the common phrase contemplate suicide.

to cogitate

I don't hear this word a lot. According to Google, it can be used intransitively, so you don't have to be cogitating about anything in particular. The other words here generally require a "target" to make sense.

to deliberate [on]

means the same as contemplate. When I hear this word, I think of court proceedings or meetings ("the jury will deliberate... etc.").

to ruminate

I don't hear this in speech very much. In my opinion it's a "less serious" version of contemplate.

to dwell on

means to think about something over and over. It could be the consequences of a decision not yet made, a decision that just has been made, or it could be going over past events in your mind. Dwell on can have a negative connotation, possibly that what you are dwelling on is bothering you or haunting you.

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So, I would answer like this:

("depth 10k worths" doesn't make sense to me, so the second is a guess)

I have been dwelling on my son (all day) since he left home for college.

I have been mulling over my depth 10k worths because I will have to pay it by next week but I don't have enough money. So I have to find a way.

I have been dwelling on my new school project. I don't know where to start.

The government deliberated how to stop protest on raising student fees.