[philman_36]

Okay, I'll try one more time and see if I can make this as concise as I can.
Look in any standard Hebrew lexicon, and under beth-resh-kaph you will find "bless" (and the related concept, "kneel"), while under beth-resh-qoph you will find "lightning."
I agree. The first two consonants are the same. And yet despite having different ending consonants both words sound almost the same.
Hebrew phonology
The phoneme /k/ is represented by two letters: kaf (כ) and quf (ק). Although Modern Hebrew pronunciation does not differentiate between the two, the latter was once pronounced more deeply, like the Arabic /q/.

Being as both words are so similar did one come before the other and derive from the first making one word a root of the other or are they both root words?
Language Log
The Hebrew spelling (if not the English transliteration) still reveals the historical root because of the orthographic difference between kaf (כ) and quf (ק). Thus Ehud Barak's last name is spelled with a quf (בָּרָק). (Interestingly, Barak didn't always have a name evoking lightning; he was born Ehud Brog and switched to "Barak" when he was drafted into the Israel Defense Forces.)
And if they're both root words then what do you say of the last two sentence in the link above about Ehud Barak's name being associated to lightning?

[philman_36]

ברק אובמה Barack Obama
אֵהוּד בָּרָק Ehud Barak

Try as I might I can't find anything anywhere that has the name Barak/Barack ending in anything other than a quf (ק).

[philman_36]

Besides, who would name their child "knee"? ברך

Barack...ברק
knee...ברך