I am involved in a dispute related to the forces that a dog's head is exposed to when he, of its own power, runs into a stationary object. Because of the dog's structure (this is a small dog) the head is getting pinched between the stationary object and his own back part of the body (which we believe is directly behind the head). Let's say the dog's weight is 10 kg and the head hold 20% of the mass and the rest is behind the head. At the collision it would be one force against the forehead from the object and another force toward the back of the head because of the kinetic energy from the 8 kg's that is behind the head. At the same time the parts are linked together. If I want to calculate the force on the front and back of the head How should I do? Calculate as if it are two separate bodies that collide. First the head with a mass of 2 kg that collied with the solid object and than the back part of the body with a mass of 8 kg that collied with the now stationary head.