# NCERT Class 9 Science Solutions: Chapter 10 – Gravitation Part 6 (For CBSE, ICSE, IAS, NET, NRA 2022)

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Question 12:

Q. Gravitational force on the surface of moon is only as strong as gravitational force on the Earth. What is the weight in newtons of a object on the moon and on the Earth?

Weight of an object on the moon weight of an object on the earth

Also,

Acceleration due to gravity,

Therefore, weight of a 10 kg object on the Earth

And, weight of the same object on the moon

Question 13:

A ball is thrown vertically upward with a velocity of . Calculate

Q. (i) the maximum height to which it rises.

According to the equation of motion under gravity:

Where,

Initial velocity of the ball

Final velocity of the ball

Height achieved by the ball

Acceleration due to gravity

At maximum height, final velocity of the ball is zero,

During upward motion,

Let be the maximum height attained by the ball.

Hence,

Q. (ii) the total time it takes to return to the surface of the earth.

Initial velocity of the ball

Final velocity of the ball

Height achieved by the ball

Acceleration due to gravity

At maximum height, final velocity of the ball is zero,

During upward motion,

Let be the time taken by the ball to reach the height 122.5m, then according to the equation of motion:

we get,

But,

Time of ascent Time of descent

Therefore, total time taken by the ball to return

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