In a 2D environment, I have a circle with velocity v, a stationary point (infinite mass), and I am trying to calculate the velocity of the circle after a perfectly elastic collision with the point.
This is what I've came up with:
$p$ is the position of the point
$c$ is the position of the circle
On a collision, the new velocity is $normalize(p – c) * velocity.magnitude$.
Would this approach be right? If not, how do I correctly determine the velocities after a collision?
Best Answer
Draw a line from the point through the centre of the circle at the moment of contact. The outward velocity vector of the circle after the collision is $-$ the reflection of the initial velocity vector across this line. This allows kinetic energy and angular momentum about the point to be conserved.