How to convert elastic constraint so it works as a billiard cue ball works.

[UsmanMuhammad]

Hi,

I am using this snippet from slingshot.js which has this elastic constraint. I want to make it work like billiard cue ball, that when the user pushes, it should have the elastic behavior but then it should move straight. But due to pointA it doesn't work for me.

here is the snippet:
var anchor = { x: cue.position.x, y: cue.position.y },
elastic = Constraint.create({
pointA: anchor,
bodyB: cue,
stiffness: 0.05,
render: {
lineWidth: 0.5
}
});

Events.on(engine, 'tick', function() {
if (mouseConstraint.mouse.button === -1 && (cue.position.x > 170 || cue.position.y < 330)) {
elastic.bodyB = cue;
//want to update the pointA here but not able to.
}
});

var mouse = Mouse.create(render.canvas),
mouseConstraint = MouseConstraint.create(engine, {
mouse: mouse,
constraint: {
stiffness: 0.2,
render: {
visible: false
}
}
});

World.add(world, mouseConstraint);

I know it's a rookie question to ask, but please any help would be appreciated.
Thanks