Please can you tell me HOw IRR is used and why is it used? IS it like the sensititivty analysis??

Perhaps what you find on the following site will be helpful to you. I hope that you do.

Internal Rate Of Return - IRR: Definition and Much More from Answers.com

It would be good if we did have an accounting expert on this site. I wish that we had someone like that here. But unfortunately, to my knowledge, we don't because so many of the accounting questions go unanswered. Perhaps we will have someone with that knowledge and expertise here in the future.