# NCERT Class 11 Physics Solutions: Chapter 8 – Gravitation-Part 3

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**Question 8.6:**

Choose the correct alternative:

If the zero of potential energy is at infinity, the total energy of an orbiting satellite is negative of its kinetic/potential energy.

The energy required to launch an orbiting satellite out of earth’s gravitational influence is more/less than the energy required to project a stationary object at the same height (as the satellite) out of earth’s influence.

**Answer:**

Kinetic energy

**Explanation:**

Total mechanical energy of a satellite is the sum of its kinetic energy (always positive) and potential energy (may be negative). At infinity, the gravitational potential energy of the satellite is zero. As the Earth-satellite system is a bound system, the total energy of the satellite is negative.

Thus, the total energy of an orbiting satellite at infinity is equal to the negative of its kinetic energy.

Kinetic energy

**Explanation:**

Less

**Explanation:**

An orbiting satellite acquires a certain amount of energy that enables it to revolve around the Earth. This energy is provided by its orbit. It requires relatively lesser energy to move out of the influence of the Earth’s gravitational field than a stationary object on the Earth’s surface that initially contains no energy.

**Question 8.7:**

Does the escape speed of a body from the earth depend on

The mass of the body,

The location from where it is projected,

The direction of projection,

The height of the location from where the body is launched?

**Answer:**

No

No

No

yes

**Explanation:**

Escape velocity of a body from the Earth is given by the relation:

Acceleration due to gravity

Radius of the Earth

It is clear from equation that escape velocity is independent of the mass of the body and the direction of its projection. However, it depends on gravitational potential at the point from where the body is launched. Since this potential marginally depends on the height of the point, escape velocity also marginally depends on these factors.

**Question 8.8:**

A comet orbits the Sun in a highly elliptical orbit. Does the comet have a constant

(a) Linear speed,

(b) Angular speed,

(c) Angular momentum,

(d) Kinetic energy,

(e) Potential energy,

(f) Total energy throughout its orbit?

Neglect any mass loss of the comet when it comes very close to the Sun.

**Answer:**

No

No

Yes

No

No

yes

**Explanation:**

Angular momentum and total energy at all points of the orbit of a comet moving in a highly elliptical orbit around the Sun are constant. Its linear speed, angular speed, kinetic, and potential energy varies from point to point in the orbit.