The correct option is **B. A satellite orbiting Earth in a circular path**. ### Detailed Explanation **Understanding Centripetal Force:** Centripetal force is the force that keeps an object moving in a circular path. It acts towards the center of the circle around which the object is moving. This force is necessary because, without it, the object would move in a straight line due to inertia (Newton's first law of motion). **Why Option B is Correct:** - A satellite in orbit around Earth is constantly changing direction as it moves along a circular path. This change in direction means that the satellite is accelerating, even if its speed remains constant. - The gravitational force between the Earth and the satellite acts as the centripetal force. It pulls the satellite towards the center of the Earth, allowing it to maintain its circular orbit. - The formula for centripetal force (\(F_c\)) can be expressed as: \[ F_c = \frac{mv^2}{r} \] where: - \(m\) is the mass of the satellite, - \(v\) is the orbital speed of the satellite, - \(r\) is the radius of the circular path (distance from the center of the Earth to the satellite). ### Why the Other Options are Incorrect: **Option A: A car accelerating in a straight line on a flat road** - This scenario does not involve circular motion. The car is moving in a straight line, and while it may be accelerating, there is no centripetal force acting on it. Instead, the forces acting on the car are related to its acceleration (like friction and engine force), not centripetal force. **Option C: A ball thrown vertically upwards** - When a ball is thrown vertically, it moves up against the force of gravity until it reaches its peak and then falls back down. This motion is linear, not circular, and thus does not involve centripetal force. The only forces acting on the ball are gravitational forces, which do not provide a centripetal effect. **Option D: A swimmer pushing off the wall of a pool to move forward** - When a swimmer pushes off the wall, they are exerting a force that propels them forward in a straight line. This action does not involve circular motion, and therefore, there is no centripetal force at play. The swimmer's motion is linear, and the forces involved are related to the push against the wall and the resistance of the water. ### Summary of Key Points: - **Centripetal Force** is necessary for circular motion, acting towards the center of the circular path. - **Correct Answer**: A satellite orbiting Earth experiences centripetal force due to gravity, allowing it to maintain its circular orbit. - **Incorrect Options**: - A car accelerating straight does not involve circular motion. - A ball thrown vertically is also linear motion, not circular. - A swimmer pushing off the wall moves in a straight line, not in a circle. - Remember that centripetal force is always directed towards the center of the circular path, and it is crucial for maintaining circular motion.