Question:
Whenever a body is thrown up with a certain velocity,the upward motion is opposed by gravitational pull of earth and also by the resistance of air.
Therefore, velocity of the body goes on decreasing. When this velocity becomes zero,the body cannot rise further.It has attained,what is called ‘maximum height’.From this height,the body begins to fall downwards under the action of gravity.
Read the above passage and answer the following questions:
(i) At the highest point,what are the velocity and acceleration of the body?
(ii) What is the maximum height attained by a body thrown upwards with a velocity of 19.6 m/s ? Take g =.
(iii) What values in life do you learn from this concept ?
Answer:
(i) At the highest point,velocity of body = zero,and acceleration of body = + g = ,in the downward direction.
(ii) Here,u=,a = - g = -.
5 = h = ?, v = 0
From = 2 as ; 0 - = 2 (- 9.8)h
h==19.6 m
(iii) The upward motion of a body is opposed by gravitational pull of earth. Similarly,your progress and prosperity in life are opposed by so many factors. Just as a body has to work against gravity for rising.upwards,every iodividual has 10 work against many odds and obstacles to rise in life. Consistent efforts alone can surmount the impediments and help you achieve your goal.
Gravitation
Q 1.
Two objects of masses
having the same size are dropped simultaneously from heights
respectively.Find out the ratio of time they would take in reaching the ground.Will this ratio remain the same if (1) one of the objects is hollow and the other one is solid and (ii) both of them are hollow,size remaining the same in each case.Give reason.
Q 2.
Is mass a scalar quantity?
Q 3.
Comment on application of Newton’s third law of motion to gravitation.Illustrate by examples.
Q 4.
State and explain universal law of gravitation.What is its importance ?
Q 5.
Fill in the blanks :
Heliocentric model was proposed by ______.
Q 6.
Write the standard equations of motion when an object is thrown upwards with some initial velocity?
Q 7.
If the distance of Earth from the Sun were half the present value,how many days will make one year ?
Q 8.
A stone falling towards Earth also attracts the Earth with the same force.Is it true ?
Q 9.
How are gravitation and gravity related ?
Q 10.
Can you calculate density of Earth from Newton’s law of gravitation ?
Q 11.
Whenever a body is thrown up with a certain velocity,the upward motion is opposed by gravitational pull of earth and also by the resistance of air.
Therefore, velocity of the body goes on decreasing. When this velocity becomes zero,the body cannot rise further.It has attained,what is called ‘maximum height’.From this height,the body begins to fall downwards under the action of gravity.
Read the above passage and answer the following questions:
(i) At the highest point,what are the velocity and acceleration of the body?
(ii) What is the maximum height attained by a body thrown upwards with a velocity of 19.6 m/s ? Take g =
.
(iii) What values in life do you learn from this concept ?
Q 12.
Why do sewing needles and all pins have a sharp pointed tip?
Q 13.
What is the gravitational acceleration of a spaceship at a distance equal to two Earth’s radius from the centre of the Earth ?
Q 14.
A boy on a clif£ 49 m high drops a stone.One second later,he throws a second stone after the first.They both hit the ground at the same time. With what speed did he throw the second stone ?
Q 15.
Can you calculate mass of Earth from Newton’s law of gravitation ?
Q 16.
Distinguish between mass and weight.
Q 17.
Explain what is meant by ‘free fall’and acceleration due to gravity.
Q 18.
Fill in the blanks :
Weight of an object is the product of ______ and ________.
Q 19.
Who measured the value of G first time, experimentally?
Q 21.
The distance between two objects is doubled. What happens to gravitational force between them
Q 22.
Does gravitational force between two objects depend on medium between them ?
Q 23.
What is the SI unit of weight ?
Q 24.
When a ball is thrown upwards, it falls back to the ground. Name the force which makes it fall.
Q 25.
If the distance between two masses is increased by a factor of 4,by what factor would the mass of one of them have to be altered to maintain the same gravitational force ?
Q 26.
Why is the weight of an object on the Moon (l/6)th its weight on the Earth ?
Q 27.
What is the acceleration of free fall ?
Q 28.
What do we call the gravitational force between the Earth and an object ?
Q 29.
What is value of ‘g’ on Earth ?
Q 30.
Why is G called the Universal Constant?
Q 33.
Two bodies A and B having masses 2 kg and 4 kg respectively are separated by 2 m.Where should a body of mass 1 kg be placed so that the gravitational force on this body due to bodies A and B is zero ?
Q 34.
What do you mean by acceleration due to gravity ?
Q 35.
Then why Is the Earth not seen moving towards the stone ?
Q 36.
A body is just dropped from a height What is its initial velocity ?
Q 37.
Compare gravitational force between light objects and heavy objects.
Q 38.
Write down the equations of motion of objects under the influence of gravitational force of Earth.Explain the meaning of the symbols used.
Q 39.
In Fig.,the line that joins a planet to the sun sweeps out areas
,
in time intervals 6 weeks,3 weeks and 2 weeks respectively.How are
,
realted ?
Q 40.
Fill in the blanks :
The mass of an object _____ (varies/does not vary) on the earth as well as on the moon. But its weight is ______(same/different) on both places.
Q 41.
A stone is released from the top of a tower of height 19.6 m. Calculate its final velocity just before touching the ground.
Q 42.
Name the scientist who identified the relation about force of gravitation. Name the law.
Q 44.
A solid weighs 80g in air, 64g in water. Calculate the relative density of solid.
Q 45.
The mass of Sun is
kg and mass of Earth is
kg. If the distance between the centres of Sun and Earth is
km,calculate the force of gravitation between them.
Q 46.
State the universal law of gravitation.
Q 47.
What are the differences between the mass of an object and its weight ?
Q 48.
Calculate the force of gravitation between the Earth and the Sun,given that the mass of the Earth =
kg and mass of the Sun =
kg. The average distance between the two is
m.
Q 49.
What is the usual shape of orbits of planets around the Sun ?
Q 50.
A body is projected upwards. What is its velocity at maximum height
