How to Drag and throw object forcefully in Unity2D - unity3d

Question

I'm new in Unity 2D i want to drag & throw my game object forcefully. basically i have three game object and when i drag anyone off then to upward i should be throw forcefully on that direction.
can anyone tell me how to do it?
i have tried this code but when i'm going to click to drag my game object then it throws directly without dragging it.
here is my code
private Rigidbody2D rb;
private float jumpForce = 700f;
private bool jumpAllowed = false;
float deltaX, deltaY;
string button_name = "";
// Use this for initialization
private void Start ()
{
Debug.Log("Started");
rb = GetComponent<Rigidbody2D> ();
PhysicsMaterial2D mat = new PhysicsMaterial2D();
mat.bounciness = 0.75f;
mat.friction = 0.4f;
GetComponent<CircleCollider2D>().sharedMaterial = mat;
}
// Update is called once per frame
private void Update ()
{
Debug.Log("Update");
if (Input.touchCount > 0)
{
Touch touch = Input.GetTouch(0);
Vector2 touchPos = Camera.main.ScreenToWorldPoint(touch.position);
switch (touch.phase)
{
case TouchPhase.Began:
if (GetComponent<Collider2D>() == Physics2D.OverlapPoint(touchPos))
{
deltaX = touchPos.x - transform.position.x;
deltaY = touchPos.y - transform.position.y;
jumpAllowed = true;
rb.freezeRotation = true;
rb.velocity = new Vector2(0, 0);
rb.gravityScale = 0;
GetComponent<Collider2D>().sharedMaterial = null;
}
break;
case TouchPhase.Moved:
if (GetComponent<Collider2D>() == Physics2D.OverlapPoint(touchPos) && jumpAllowed)
{
rb.MovePosition(new Vector2(touchPos.x - deltaX, touchPos.y - deltaY));
}
break;
case TouchPhase.Ended:
jumpAllowed = false;
rb.freezeRotation = false;
rb.gravityScale = 2;
PhysicsMaterial2D mat = new PhysicsMaterial2D();
mat.bounciness = 0.75f;
mat.friction = 0.4f;
GetComponent<CircleCollider2D>().sharedMaterial = mat;
break;
}
}
}

Answer 1

First, there's one mistake
rb.MovePosition(new Vector2(touchPos.x - deltaX, touchPos.y - deltaY));
should be
rb.MovePosition(new Vector2(touchPos.x + deltaX, touchPos.y + deltaY));
There's also another issue, MovePosition doesn't affect the object velocity at all. If you stop using MovePosition, the object will just fall without keeping any energy from the previous movement.
You could simply store the previous position every movement, and do this on TouchPhase.Ended:
rb.velocity = (rb.position - prevPosition) / Time.deltaTime;
Simply put, this calculates the velocity that was required to accomplish the last movement, and apply it to the rigidbody.