# NCERT Class 9 Science Solutions: Chapter 10 – Gravitation Part 9

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Question 18:

A ball thrown up vertically returns to the thrower after find

Q. (a) the velocity with which it was thrown up,

**Answer:**

29.4

Time of ascent is equal to the time of descent. The ball takes a total of 6 s for its upward and downward journey.

Hence, it has taken 3 s to attain the maximum height.

Final velocity of the ball at the maximum height,

Acceleration of motion, will give,

Hence, the ball was thrown upward with a velocity of

Q. (b) the maximum height it reaches, and

**Answer:**

44.1 m

Let the maximum height attained with a velocity of .

Initial velocity during the upward journey,

Final velocity,

Acceleration due to gravity,

From the equation of motion,

Q. (c) Its position after

**Answer:**

Ball attains the maximum height after. After attaining this height, it will start falling downwards.

In this case,

Initial velocity,

Position of the ball after of the throw is given by the distance travelled by it during its downward journey in

Equation of motion, will give,

Total height

This means that the ball is above the ground after second.