I am new to learning the piano ... i have some sheet music for piano ... my friend plays the violin and piano ... he said the same sheet music for the piano can be used to play the violin ... i toguht you had to get separate sheet music for every instrument

Well, yes and no.
You have to get diffent music depending on the key of the instrument.
For example, the clarinet is in the key of b-flat and the piano is in the key of c. You cannot use the same music for both of them.
I am not sure on this, but I think because the way the violin is turned (with the four strings in fifths) you can play that music on the piano.
I hope that makes scence. If it dosen't, just ask me a question
-aKari

Hi iseeghosts.....I think your friend is right....I think two separate sheet musics are used just to make it easier for each musician to read. Also, sometimes the piano might be playing an accompaniment which will be different notes from the violin.