There are many who believe that Jesus was part man and part God,during His brief stay on earth. 

The idea that Jesus was both man and god is ludicrous and they worship Jesus  Christ as a God, and  they think of the God as being composed of three parts..Father, Son and Holy Ghost. They are the same ones wh o consign His mother Mary to life of perpetual virginity!

The Trinjity is not a single entity.  Rather, God, the Father stands alone, preeminate, what I think of as an incredible spiritual energy, without form that we would recognize, that I choose to call the Supreme Presence, and always refer to as "Father", when I go to Him.  Eminating from Him is the Son..the Christ as we recognize Him, and the Holy Ghost/Spirit, that Jesus referred to as the Great Comforter.

Alright, we should realize that Jesus was wholly human, on earth.  So, how was He "sinless"?

That's the "bugaboo". For we know that NO human is able to go through, life, no matter how long..if only 30+ years, without "missing the mark"..sinning, 

How do we explain this then that Jesus never commited a sin?

I believe that the only way, was for Him to be filled with the Holy Spirit of God, which provided Him with an incredible energetic force and prevented Him from sinning..In other words, He was constantly connected with the Father.

I think His possessing of "energy" is proven when that woman simply touched his garment, reaching out for supplication, and He was aware that someone touched Him. This awarenesss could come about by His feeling a slight change in this energetic force..maybe a tingling or a slight dimunition.

There were instances during His time on earth, where He exhibited real humanity.

 One such instance was in the Garden of Gesthemane, where He asked to have the "cup" removed from Him..not having to undergo the crucifixion.  He even sweated blood over this.  But then he relented and stated that God's will  be done. I believe it was at that moment that the Spirit took over in HIm.

I visited the "Garden of Gesthemane" during my trip to Jerusalem.  To me it was too pretty.   Obviously, if chosen as the holy sight, it would be made presentable for tourists, but I couldn't stop believing it was located too close to the city.  If He was going to hide, in order to collect His thoughts and avoid confrontation until the right time, He would've picked a  more secluded location. 

Another instance when He became very "human", was on the "cross", not long before He succumbed, when He "rebuked" God, by crying out "..why have thou abanddoned me?" The Holy Spirit had left Him to suffer the agonies and indignities alone, and God had literally turned His back on Him.  He was made to suffer the physical agonies  as any human would, with the  addition of bearing the sins of the world.  The "sinless" one was made to experience the emotions and the realty of every heinous sin imaginable.

Why?

By doing so, He fulfilled the mission of the Father, as a dutiful Son, so that we would be saved, and justified of our sins.

How do we know this..how do we kinow that he was fully human?

Because our teacher, Paul said so.."He emptied Himself.." bobnpaul