# NCERT Class 11 Physics Solutions: Chapter 8 – Gravitation-Part 5

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Question 8.12:

A rocket is fired from the earth towards the sun. At what distance from the earth’s centre is the gravitational force on the rocket zero?

Mass of the sun,

mass of the earth

Neglect the effect of other planets etc. (orbital radius).

Mass of the Sun,

Mass of the Earth,

Mass of the rocket

Let x be the distance from the centre of the Earth where the gravitational force acting on satellite P becomes zero.

From Newton’s law of gravitation, we can equate gravitational forces acting on satellite P under the influence of the Sun and the Earth as:

Question 8.13:

How will you ‘weigh the sun’, that is estimate its mass? The mean orbital radius of the earth around the sun is .

Orbital radius of the Earth around the Sun, Time taken by the Earth to complete one revolution around the Sun,

Universal gravitational constant,

Thus, mass of the Sun can be calculated using the relation,

Hence, the mass of the Sun is

Question 8.14:

A Saturn year is the earth year. How far is the Saturn from the sun if the earth is away from the sun?

Distance of the Earth from the Sun,

Time period of the Earth

Time period of Saturn,

Distance of Saturn from the Sun

From Kepler’s third law of planetary motion, we have

For Saturn and Sun, we can write,

Hence, the distance between Saturn and the Sun is