Where does the gravitational energy come from We know that when a mass is pulled by gravitation it's kinetic energy increases.
This is also the case when a photon is being radiated towards a massive body,its wave length decreases and it's energy increases. Since I know that energy is conserved,my question is,where does this extra energy come from?
 A: It comes from the potential energy from gravity arising from the configuration of the objects.
When an object gains kinetic energy due to the gravitational force, the overall gravitational potential energy of the system decreases by an equal amount.
The graviational field can be thought of as "storing" work energy.  You can increase the potential energy of the system by investing energy into re-arranging the system, and you can decrease the potential energy of the system by extracting it as kinetic energy.
You can, for example, imagine taking a book from the floor and placing it on a shelf directly above the original spot.  This takes a certain amount of work, $W$.  Later, if you decide to remove the shelf and let the book fall back to the floor, the book should accumulate kinetic energy $\frac{1}{2} mv^2$ exactly equal to the original work $W$ you put in.
The "original source" of the energy that the book gains when falling, then, is the work energy that you originally invested in putting it on the shelf.  Numerically, they are equal.  The gravitational potential took that original energy, stored it, and releases back the same amount when the book falls.
