Question

as the text discusses, the conservation of linear momentum is applicable only when the system of objects is an isolated system. which of the systems listed below are isolated systems? 1. a ball is dropped from the top of a building. the system is the ball. 2. a ball is dropped from the top of a building. the system is the ball and the earth. 3. a moving billiard ball collides with a stationary billiard ball on a frictionless pool table. the system is the moving ball. 4. a car slides to a halt in an emergency. the system is the car. 5. a space probe is moving in deep space where gravitational and other forces are negligible. the system is the space probe. only 5 is an isolated system. only 1 and 3 are isolated systems. only 2 and 5 are isolated systems. only 3 and 5 are isolated systems. only 4 and 5 are isolated systems.

Explanation:

• System 1: The ball is acted on by gravity (external force from the Earth), so it is not an isolated system.
• System 2: The ball - Earth system. The gravitational force is an internal force within the system (as it is a force between the two parts of the system). There are no external forces (neglecting air resistance, which is not mentioned as a part of the system).
• System 3: The moving ball is acted on by the stationary ball (external force if we consider only the moving ball as the system).
• System 4: The car is acted on by friction (external force) as it slides to a halt.
• System 5: In deep space with negligible gravitational and other forces, the space - probe has no external forces acting on it.

Answer:

Only 2 and 5 are isolated systems.