many buses that follow routes along ipanema and copacabana reach urca - the destination is displayed and easily seen on the front of the buses, but stop about 200 meters away from the actual beach.  

bus number 512 (urca x leblon) runs along avenida portugal and stops at urca beach, alternatively directly from the botafogo metrô station bus 513 (botafogo x urca) can be taken reaching urca via avenida pasteur.

this link shows praia da urca on a wikimapia - the link as we present it is best seen using google chrome, as it might not open correctly with other browsers.