Linear velocity

I have a shooting game of bow and arrow. I want to move the arrow with some velocity in the direction it is pointed. I have accomplished it in the
following way:

Code:


      vec3 tip = {0.989,1.229,5.083};  //1. Tip of the arrow
      vec3 centre = {3.146,-1.254,3.043}; //2. Centre Location of the arrow
      vec3 result;
      sio2Vec3Diff(&tip, &centre, &result);
      sio2Normalize(&result, &result);
      _SIO2Spear->_btRigidBody->setLinearVelocity(( btVector3( result.x*40.0, result.y*40.0, result.z*40.0) ));


Using 1 & 2 I determine the direction of the vector , normalize it and then apply velocity. However the result is not satisfactory. Considering
arrow is a long object ( not like a sphere), is there any other method to move it in the desired direction with the tip of the arrow pointing in the
desired direction?

Thank you.

Cheers,
Rahul.

Check sio2rotate3d this will allow you to calculate a forward vector sound an arc.