Learn English – Import and export preposition usage

There isn't going to be a quick way to match up propositions. There are some general rules that fit a majority of the cases but the exceptions abound.

Unfortunately, changing prepositions around will have drastic effects on its meaning. Instead of trying to catch and explain all cases, I have decided to simply use your examples and explain what they mean:

I worked on a project

"On" is typical here and will be correct most of the time. Working on a project implies doing work related to the project and is similar to working on a house or working on a letter. You are performing an action (working) on an object (the project).

The tricky side of "on" comes with phrases like, "I worked on a farm." Working "on a farm" means doing work while located on a farm instead of working on the object of a farm.

A good test is to try replacing "worked on" with "completed": "I completed a project" or "I completed a house" sound fine while "I completed a farm" drastically changes its meaning.

I worked in a project

Working "in" something is more akin to being located inside of the object. "I worked in a building." A "project" can certainly contain things and so you can technically work "in" a project.

When I was at the university I studied math

Here, "at" is mostly referring to your physical location. You did work while being located at the university. This generally refers to students enrolled in the university but also applies to people who were just visiting or possibly working there in a way unrelated to learning (such as the janitor.)

When I was in the university I studied math

Again, "in" here implies being "inside of" or "contained by" the university. To say, "I am in university" generally means to be enrolled in one of the university's programs. Unfortunately, it can also mean being physically inside of the university buildings... so I am not helping much.

The most common case is to say, "When I was at..." but there is a mix of things happening here. People will ask you "Where do you go to school?" The importance seems to fall on the physical location but this usage does not cover strange exceptions such as enrolling in classes over the internet where you never move from your chair but are considered "at" a particular university.

In any case, I hope this helped somewhat.

wel·come

noun

• 1. an instance or manner of greeting someone. "you will receive a warm welcome" synonyms: greeting, salutation

Exclamation

• 1 used to greet someone in a glad or friendly way. "welcome to the Wildlife Park"

verb

• 1 greet (someone arriving) in a glad, polite, or friendly way. "hotels should welcome guests in their own language"

• 2 be glad to entertain (someone) or receive (something). "we welcome any comments"

• 3 react with pleasure or approval to (an event or development). "the bank's decision to cut its rates was widely welcomed"

adjective

• 1. (of a guest or new arrival) gladly received. "visitors with disabilities are always welcome"

• 2 very pleasing because much needed or desired. "after your walk, the cafe serves a welcome pot of coffee"

• 3 allowed or invited to do a specified thing. "anyone is welcome to join them at their midday meal"

• 4 used to indicate that one is relieved to be relinquishing the control or possession of something to another. "the job is all yours and you're welcome to it!"

As for your examples: #1 is grammatically correct, but unlikely. Instead, you would say (present tense, speaking to John) "We welcome you, John" or (past tense, speaking to someone else) "We welcomed John."

In #2, some other word or punctuation is needed to make sense. Assuming "Veeru" is a place, and "junior" is a certain person (e.g. a junior in high school): "Welcome to Veeru, junior(s)!" or "We welcome juniors to Veeru."

And finally, the answer to your question: You don't need "to" in the first one because John is the Direct Object of the verb "welcome". In the second, "junior is (apparently) the Direct Object, whereas "Veeru" is (apparently) the Indirect Object, so it requires "to ".