How to control the speed of the projectile motion?

Questions & Answers
1

I have created a simple script which will move the sphere in a projectile motion.

public class ProjectileTest : MonoBehaviour 
{
	public float power;
	public float speed = 1f;
	void OnGUI ()
	{
		if(GUI.Button(new Rect(100, 100, 100, 50), "Reset"))
		{
			Application.LoadLevel(Application.loadedLevel);
		}
	}

	void Update ()
	{
		if (Input.GetMouseButtonDown (0)) 
		{

		}
		if (Input.GetMouseButton (0)) 
		{
			power+=0.1f;
		}
		if (Input.GetMouseButtonUp (0)) 
		{
			Debug.Log("Power : "+power);
			if(power > 10)
				power = 10f;
			transform.rigidbody.isKinematic = false;
			Vector3 forceVector = new Vector3(1, 1, 0);
		
			transform.rigidbody.velocity = forceVector * power * speed;
		}
	}
}

Now as the question says, how can i control the speed of the projectile motion?

The sphere should move in the projectile but with a factor of speed.

Like sometimes i want it to move fast or slow but the projectile path should be same.

2

To change the speed, simply change the ‘speed’ or ‘power’ variable. But that does not get what you specify in the latter half of your statements. Having a projectile follow the path whether the projectile is fast or slow, breaks physics. The only way I can see with involve some somewhat complicated math and varying the gravity on a throw-by-throw basis. You could also abandon the use of the Rigidbody, and calculate the path directly and move the projectile using the Transform. A sine function makes a nice arc.