Inelastic collision only moving object to the right

Question

My Rocket is hitting this Inertia object, as defined in handleCollision. I'm passing in a rocket which has a .r value for its theta and .power for its magnitude.

I'm wanting to update my .rotation & .magnitude according to an inelastic collision as defined by Wikipedia

When colliding from the left, my Inertia moves to the right.

But when colliding from the right it errors and moves exactly 180 degrees off. So if the rocket is up and right at a 45 degree angle from the inertia object, the object will move up and right at a 45 degree angle.

What am I missing here? I thought it might be an issue with the atan function so I converted by the y component & x component of the vector to radians first, same issue.

handleCollision(rocket) {
    var angle = rocket.r * Math.PI / 180.0;
    var rr = this.rotation * Math.PI / 180;

    var rocketVector = {'x' : r.power * Math.cos(angle), 'y' : r.power * Math.sin(angle)};
    var inertiaVector = {'x' : this.magnitude * Math.cos(rr), 'y' : this.magnitude * Math.sin(rr)};

    var rMass = 10;
    var shipMass = 10;

    var x = (rMass * rocketVector.x) + (shipMass * inertiaVector.x);
    var y = (rMass * rocketVector.y) + (shipMass * inertiaVector.y);
    var xDividedByMass = x / (rMass + shipMass);
    var yDividedByMass = y / (rMass + shipMass);

    var yRadians = (yDividedByMass * Math.PI / 180);
    var xRadians = (xDividedByMass * Math.PI / 180);
    var theta = Math.atan( yRadians / xRadians);

    theta = theta * 180 / Math.PI;
    console.log(theta);

    var hypotenuse = Math.sqrt((xDividedByMass * xDividedByMass) + (yDividedByMass * yDividedByMass));
    this.magnitude = hypotenuse;
    this.rotation = theta;
    if (this.rotation < 0) {
        this.rotation += 360;
    } else if (this.rotation > 360) {
        this.rotation -= 360;
    }
}

Answer 1

If xDividedbyMass>0, you are great because you are quadrant I or IV where arctangent kicks out its values. If you do not like the negative angle, okay add 360 like you did. But if x<0 and y>0, you will get a negative angle and want to add 180 to get to Q II (tangent has a period of 180). And if x<0, and y<0, you are in QIII and again arctan gives you something in Q1 to which you must add 180. The logic will look something like this.

if ((x > 0) && (y<0)) {
    this.rotation += 360;
} else if (x<0) {
    this.rotation += 180;
}