Hi, I was just wondering, is mechanical energy conserved when two cars of equal mass and moving at equal speed collide head-on and in the process both come to rest? I'm inclined to say it isn't conserved because kinetic energy is converted into other forms of energy (e.g. heat and sound) during the collision. And how about when the bicycle rider ceases to pedal and her bicycle coasts along the path until it comes to rest? Is mechanical energy conserved there? I think because of friction, it isn't conserved... Please correct me if i'm wrong. Many thanks.