The movie's musical score was composed by Brian Tyler (who composed Fast and Furious 3, 4, 5, and 7 lol). It is part of his original score made for the movie.
If you mean the soft, sad piece in the first few seconds, it is actually found on the Fast & Furious 4 soundtrack as the very last track (since the plot of Fast Five picks up immediately where Part 4 ended), called "Judgment": www.youtube.com/watch
Interestingly enough, that piece features a few seconds of what is called the "Brian and Mia" theme, written for Paul Walker and Jordana Brewster's characters in the series. It kind of ended up becoming the main theme of the movies since Part 4, which is fitting since --- if you think about it --- their romance in Part 1 formed the foundation for the entire franchise's story.
1. "How We Roll (Fast Five Remix)" (featuring J-Doe, Reek da Villian and Busta Rhymes) Don Omar 2. "Desabafo / Deixa Eu Dizer" Marcelo D2 and Claudia 3. "Assembling the Team" Brian Tyler 4. "L. Gelada-3 Da Madrugada" MV Bill 5. "Carlito Marron" Carlinhos Brown 6. "Han Drifting" Hybrid 7. "Million Dollar Race" Edu K and Hybrid 8. "Mad Skills" Brian Tyler 9. "Batalha" ObandO and DJ Harris 10. "Danza Kuduro" (featuring Lucenzo) Don Omar 11. "Follow Me Follow Me (Quem Que Caguetou?) (Fast 5 Hybrid Remix)" Tejo, Black Alien and Speed 12. "Fast Five Suite" Brian Tyler 13. "Furiously Dangerous" (featuring Slaughterhouse and Claret Jai) Ludacris