Floats after jump

Hello

Please see my code.

When i jump diagnollay it looks sort of ok, but if i just press the jump so the player makes a straight vertically jump, then when he falls down he just floats slowly towards the ground..

I can move the right and left keys to make the fall faster for some reason.

Please advice..

Code (CSharp):

1.  if(Input.GetKey("space") && IsGrounded == true || Input.GetKey("up") && IsGrounded == true)
2.         {
3.             Debug.Log("JUMP PRESSED");
4.             //jump
5.             //gameObject.GetComponent<Rigidbody2D>().AddForce(new Vector2(0f, 1000f), ForceMode2D.Impulse);
6.             // Vector2 movement = new Vector2(myRB.velocity.x, jumpPower);
7.             //myRB.velocity = movement;
8.             myRB.velocity = Vector2.up * (jumpPower) * Time.fixedDeltaTime;
9.              //myRB.velocity = new Vector2(myRB.velocity.x,  jumpPower * Time.fixedDeltaTime);
10.              animator.Play("Player_Jump");
11.         }