I have got a basic knowledge about the Unity 3D platform but I coding in Unity has not been that easy for me. For the simple reason I can see is, I cannot understand which function to use for what purpose, for example, velocity, angular velocity or torque. My question is do I need to learn Physics and Trignometry to properly learn the usage of functions in Unity script. What level of knowledge should I need to poses with respect to Physics and Trignometry in order to properly understand the code in Unity? Please be specific as I am not a science student and I have really very basic knowledge in Unity.
Well, you do need a basic understanding of physics, but I mean like what they teach in physics class in highschool. Assuming you went to highschool, then no there isn't any additional knowledge of physics that you need as a prerequisite.
That said, you're going to be learning a number of new concepts and/or applying concepts in ways that are new, because there frankly aren't many other places other than game development where that stuff would come up. I mean sure, high-end car engineering for example, but it's hardly the case that you need a degree in mechanical engineering before you can program a game.
Don't worry that you're missing prerequisite knowledge, but do accept that you're going to encounter unfamiliar concepts, so you're going to have to lookup what they mean and then spend lots of time experimenting.
Now that's with regards physics. As for trigonometry, that's a bit more crucial. Again, not much more than what they teach in highschool, but a lot of people reject even that level of math and you're going to need to be comfortable with things like sines and the Pythagorean Theorum. Depending on exactly what you program, you might also need to use some 3D math concepts, but again it's not really a prerequisite and more stuff you can learn as you go.
Here's one good resource http://blog.wolfire.com/2009/07/linear-algebra-for-game-developers-part-1/