Projectile Motion

Question: What is the ball's minimum speed?

Script

<script language="JavaScript">
function initApplet(){

document.animator.setDefault();
document.animator.setTimeInterval(0,6);
document.animator.setPixPerUnit(5);
document.animator.setGridUnit(2);
document.animator.shiftPixOrigin(-100,-100);
id=document.animator.addObject("circle","r=10");
document.animator.setTrajectory(id,"(8.55*t)","(23.49*t-4.9*t*t)");
document.animator.setRGB(id,255,0,0);
document.animator.forward();

}
</script>

Credits:
Problem by Galileo Galilei
Script by Wolfgang Christian