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In the following, what are the quantities which that are conserved?

#### Options

Linear momentum of planet

Angular momentum of planet

Total energy of planet

Potential energy of a planet

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#### Solution

**Total energy of planet**

**Explanation:**

Since there is a net force acting on the planet, its velocity changes which mean its linear momentum changes. In fact, the absolute value of linear momentum changes too since the planet’s speed is variable as it goes around in its elliptical orbit. So the linear momentum of the planet is not conserved. But the angular momentum about the sun is conserved. Since the torque of gravitational force is zero.

The total mechanical energy remains constant for isolated system objects that interact with conservative forces. So, the total energy of the system of planet is conserved. The single energy of the planet is not conserved.

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