Tips and tricks

Choose your frame of reference
Set up a coordinate system and define your velocities with respect to that system.It is usually convenient to have the x axis coincide with one of the initial velocities.
In your sketch of the coordinate system, draw and label all velocity vectors and include all the given information.
Write expressions for the x and y components of the momentum of each object before and after the collision. Remember to include the appropriate signs for the components of the velocity vectors.

Choose your frame of refrence.KE will differ in each refrence frame while PE will remains constant. Define your system, which may include two or more interacting particles, as well as springs or other systems in which elastic potential energy can bestored. Choose the initial and final points.

Draw a neat diagram of the system.
Firstly consider the origin of the forces acting on the each object.To do this find out the field forces acting on the each object.Wherever contact in available account the contact force carefully
Isolate the body whose motion is to be analyzed. Draw a free-body diagram for this body. For systems containing more than one objects, draw separate free-body diagrams for each objects

An object is said to be in state of motion if its position changes with the passage of time. If the position of the object does not change with the passage of time then the object is said to be at rest. We have now define what is motion and to describe it we consider simplest form of motion that is motion of any object in one dimension for example car moving on the road. To determine the position of car at different times , we could measure its distance from starting point and record all these observations. These observations can be recorded in form of a table or we can draw a distance versus time graph for the motion of the car and see how it is moving.