A g (pronounced "gee") is a unit of acceleration. Notice it is italicized. This is so it won't be confused with g (grams). 1 g = 9.8 m/s2. Typically a person will black out if they experience an acceleration of 4 to 6 g for more than a few seconds.
Determine how fast an object must be going if it is to experience a centripetal acceleration of 5.1 g while moving in a circular path of radius 11 m.