Class 9 Science - Chapter Gravitation NCERT Solutions | A ball thrown up vertically returns to t
A ball thrown up vertically returns to the thrower after 6 s. Find
(a) the velocity with which it was thrown up,
(b) the maximum height it reaches, and
(c) its position after 4 s.
The ball takes a total of 6 s for its upward and downward journey.
Time taken to reach maximum height = 6 / 2 = 3 s
Hence, it has taken 3 s to attain the maximum height
(a)
Let initial velocity = u m/s
Final velocity of the ball at the maximum height, v = 0 m/s
Acceleration due to gravity, g = −9.8 m s−2
Equation of motion
v = u + gt
0 = u + (−9.8 × 3)
u = 9.8 × 3 = 29.4 ms−1
Hence, the ball was thrown upwards with a velocity of 29.4 m s−1.
(b)
Let the maximum height attained by the ball = h
Initial velocity during the upward journey, u = 29.4 m/s
Final velocity, v = 0 m/s
Acceleration due to gravity, g = −9.8 m s−2
From the equation of motion,
(c) Ball attains the maximum height after 3 s. After attaining this height, it will start falling downwards.
In this case,
Initial velocity, u = 0 m/s
Position of the ball after 4 s of the throw is given by the distance travelled by it during its downward journey in 4 s − 3 s = 1 s.
Equation of motion,
s = 0 x 1 + ½ x 9.8 x 12
s = 4.9 m
Total height = 44.1 m
This means that the ball is 39.2 m (44.1 m − 4.9 m) above the ground after 4 seconds.
More Questions From Class 9 Science - Chapter Gravitation
- Q:-
What happens to the force between two objects, if
(i) the mass of one object is doubled?
(ii) the distance between the objects is doubled and tripled?
(iii) the masses of both objects are doubled? - Q:-
Why is the weight of an object on the moon 1/6th its weight on the earth?
- Q:-
A stone is released from the top of a tower of height 19.6 m. Calculate its final velocity.
- Q:-
Gravitational force acts on all objects in proportion to their masses. Why then, a heavy object does not fall faster than a light object?
- Q:-
You find your mass to be 42 kg on a weighing machine. Is your mass more or less than 42 kg?
- Q:-
Why does an object float or sink when placed on the surface of water?
- Q:-
What is the acceleration of free fall?
- Q:-
The volume of a 500 g sealed packet is 350 cm3. Will the packet float or sink in water if the density of water is 1 g cm-3? What will be the mass of the water displaced by this packet?
- Q:-
A ball is thrown vertically upwards with a velocity of 49 m/s. Calculate
(i) the maximum height to which it rises,
(ii) the total time it takes to return to the surface of the earth. - Q:-
The earth and the moon are attracted to each other by gravitational force. Does the earth attract the moon with a force that is greater or smaller or the same as the force with which the moon attracts the earth? Why?
Popular Questions of Class 9 Science
- Q:-
Which of the following has more inertia: (a) a rubber ball and a stone of the same size? (b) a bicycle and a train? (c) a five-rupees coin and a one-rupee coin?
- Q:-
Which of the following are matter?
Chair, air, love, smell, hate, almonds, thought, cold, cold-drink, smell of perfume.
- Q:-
A force of 7 N acts on an object. The displacement is, say 8 m, in the direction of the force (Fig. 11.3). Let us take it that the force acts on the object through the displacement. What is the work done in this case?
- Q:-
What is meant by a pure substance?
- Q:-
How does the sound produced by a vibrating object in a medium reach your ear?
- Q:-
In a reaction, 5.3 g of sodium carbonate reacted with 6 g of ethanoic acid. The products were 2.2 g of carbon dioxide, 0.9 g water and 8.2 g of sodium observations are in agreement with the law of conservation of mass.
sodium carbonate + ethanoic acid → sodium ethanoate + carbon dioxide + water
- Q:-
What are canal rays?
- Q:-
State any two conditions essential for good health.
- Q:-
How is our atmosphere different from the atmospheres on Venus and Mars?
- Q:-
Who discovered cells, and how?
Recently Viewed Questions of Class 9 Science
- Q:-
Explain, why is it difficult for a fireman to hold a hose, which ejects large amounts of water at a high velocity.
- Q:-
What would happen if the plasma membrane ruptures or breaks down?
- Q:-
If Z = 3, what would be the valency of the element? Also, name the element.
- Q:-
How will you find the valency of chlorine, sulphur and magnesium?
- Q:-
Can you name the two organelles we have studied that contain their own genetic material?
- Q:-
Two children are at opposite ends of an aluminium rod. One strikes the end of the rod with a stone. Find the ratio of times taken by the sound wave in air and in aluminium to reach the second child.
- Q:-
Suppose you and your friend are on the moon. Will you be able to hear any sound produced by your friend?
- Q:-
Calculate the wavelength of a sound wave whose frequency is 220 Hz and speed is 440 m/s in a given medium.
- Q:-
How do you differentiate between capture fishing, mariculture and aquaculture?
- Q:-
A baby is not able to tell her/his caretakers that she/he is sick. What would help us to find out
(a) that the baby is sick?
(b) what is the sickness?
- All Chapters Of Class 9 Science
- All Subjects Of Class 9