Last time cannonball fire physics.

Hi guys I want to create a game that when I click on the screen a ball goes smoothly to my mouse position, I did a little scripting and it works but what this script of mine does is when I click on the screen it is going immediately to my mouse position, what I really want is that you have a begin position like in the middle of the screen and then whe I click it goes to my mouse position, so my mouse position is the end.

See this video to understand my problem: http://www.youtube.com/watch?v=gzdI4HmsF0Q

NOTE:

spot.position is the position is the begin position and pos is the end position. I did tried Vector3.lerp and .MovePosition and I tried AddForce but with Vector3.Lerp and MovePosition it works but as i wrote before it goes immediately to the end point which is my mouse position I want that it goes like this video:

http://www.youtube.com/watch?v=c27BK927-TE

Please take a look and help me out, this is really important for me.

Thanks in advance guys!

A little script of mine:

 void shootInput()
     {
         cannonShot.Play();
 
         journeyLength = Vector3.Distance(spot.position, pos);
 
         float distCovered = (Time.time - startTime) * 20f;
         float fracJourney = distCovered / journeyLength;
 
         depth = 15f;
 
         pos = Camera.main.ScreenPointToRay(Input.mousePosition).GetPoint(depth);
 
         Rigidbody ball = Instantiate(cannonBall, spot.position, Quaternion.identity) as Rigidbody;
 
         ball.rigidbody.MovePosition(Vector3.Lerp(spot.position, pos, fracJourney));
 
         // ball.rigidbody.AddForce(transform.forward * 200);
         // ball.rigidbody.AddForce(transform.up * 500);
 
         cannonTop.transform.LookAt(pos);
     }