Android : Reset position of object before setLinearVelocity

I'm playing around with AndEngine and its physic extension

And I can't use the setPosition properly.

I'm trying to reset the position of my object on each new user action : A touch Down, should throw the object again from its original position

What I'm doing is :

public void throwObject(){
    objectSprite.setPosition(xScene, yScene);
    objectBody.setLinearVelcity(touchXWorld, touchYWorld);
}

Note that I'm using scene coordinates for setPosition but I'm not sure what I should use here...

setLinearVelocity is working fine but the object is thrown from its current position. The setPosition() call did nothing.

Any clue on how to use it ?