When viewed from the sun, which of the following quantities stays constant during planetary motion (assuming elliptical orbits)?

Step-by-step solution

The gravitational force acting on a planet is a central force directed towards the sun. The torque about the sun is given by = r F . Since the force F is along the position vector r , the cross product is zero, yielding = 0 . According to the law of conservation of angular momentum, if the net external torque acting on a system is zero, its angular momentum remains constant. In an elliptical orbit, the distance r between the planet and the sun changes. Since angular momentum L = mvr = mr^2 is constant, the speed v