Which of these systems is NOT an “isolated system” to which conservation of momentum can be applied? 1. A ball falls freely toward the floor. (Ignore air friction.) System: the ball 2. Two masses connected by a spring oscillate on a frictionless tabletop. System: the two masses and the spring 3. A single car slips on an icy road. (Friction with the ice is negligible.) System: the car 4. A ball falls freely toward the ground. (Ignore air friction.) System: the ball and the earth 5. A billiard ball collides with another billiard ball on a level pool table. (Ignore friction with the table during the instant of the collision.) System: the two balls 6. All of these in fact are isolated systems. 7. Two cars slipping on an icy road collide with one another. (Friction with the ice is negligible.) System: the two cars
