Question:
Explain what is meant by ‘free fall’and acceleration due to gravity.
Answer:
Refer to Art 3.11, Page 159.
Gravitation
Q 1.
State Kepler’s Laws of planetary motion. How did Newton guess inverse square law ?
Q 2.
What do we call the gravitational force between the Earth and an object ?
Q 3.
Can you calculate density of Earth from Newton’s law of gravitation ?
Q 4.
The weight of an empty glass is 1 N. When completely filled with water, the glass weighs 4 N. If you now throw the water away and fill the glass partly with sand, the weight becomes 4 N. If the rest of the glass is now filled up with water, the weight becomes 6 N. What is the relative density of sand?
Q 5.
The distance between two objects is doubled. What happens to gravitational force between them
Q 6.
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 7.
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 8.
State Kepler’s Laws of planetary motion.
Q 9.
Is weight a scalar quantity?
Q 10.
What is the source of centripetal force that a planet requires to revolve around the Sun ? On what factors does that force depend ?
Q 11.
What is the value of ‘g’ at the centre of Earth ?
Q 12.
Two particles of equal mass (m) move in a circle of radius (r) under the action of their mutual gravitational attraction. Find the speed of each particle.
Q 13.
A physics teacher explains to his students in class,the subject of motion under gravity.When a body is projected upwards from the ground with a certain velocity a,the velocity goes on decreasing at a constant rate due to gravitational pull of earth.At a certain height,this velocity becomes zero.The body cannot rise further.From this maximum height,the body begins to fall and its velocity goes on increasing at the same constant rate due to gravitational pull of earth.The body would strike the ground with exactly the same velocity (v = u),with which it was thrown initially. This is on the assumption that resistance due to air is zero, either way.
Read the above passage and answer the following questions:
(i) Why is velocity of body on striking the ground the same as initial velocity of projection of the body ?
(ii) Does the body take same time to fail to ground as the time it takes to reach the maximum height ?
(iii) What values of life do you learn from this brief study ?
Q 14.
Fill in the blanks :
Weight of an object is the product of ______ and ________.
Q 15.
(a) What is the relationship between g and G?
(b) Show mathematically whether g (acceleration due to gravity on the earth) depends on the mass of the object itself or not.
(c) Show that for a given location on the surface of the earth g is almost constant.
Q 16.
Fill in the blanks :
The acceleration which causes changes only in direction of the velocity of a body is called __________ and it is always directed ___________ the circle.
Q 17.
What do you mean by acceleration due to gravity ?
Q 18.
Why will a sheet of paper fall slower than one that is crumpled into a ball ?
Q 19.
Does value of ‘g’ vary from place to place on Earth ?
Q 20.
A body is just dropped from a height What is its initial velocity ?
Q 21.
What is the SI unit of weight ?
Q 22.
Fill in the blanks :
The value of
g on the earth's surface is ______.
Q 23.
Fill in the blanks :
The SI unit of weight is _____.
Q 24.
Define weight? How it is related to mass?
Q 25.
Write the standard equations in the form when an object is dropped from a height?
Q 26.
Why is it difficult to hold a school bag having a strap made of a thin and strong string?
Q 27.
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 28.
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 29.
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 30.
State the universal law of gravitation.
Q 31.
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 32.
What is the value of G (i) on Earth (ii) on Moon ?
Q 33.
A stone falling towards Earth also attracts the Earth with the same force.Is it true ?
Q 34.
Then why Is the Earth not seen moving towards the stone ?
Q 35.
How are gravitation and gravity related ?
Q 36.
Comment on application of Newton’s third law of motion to gravitation.Illustrate by examples.
Q 37.
On earth,value of G =
.What is its value on moon,where g is nearly
th that of earth ?
Q 38.
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 39.
Fill in the blanks :
Heliocentric model was proposed by ______.
Q 40.
Fill in the blanks :
The force which keeps the object moving in a circular path is called _____ force. It always acts towards the _____.
Q 41.
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 42.
Fill in the blanks :
When objects of different masses and sizes are dropped from same height would reach the ground at ______ (same time/different times), considering negligible air resistance.
Q 43.
Fill in the blanks :
The value of
g ________ (increases/decreases) as we go upwards from the earth's surface.
Q 44.
Who measured the value of G first time, experimentally?
Q 45.
How gravitational force is different from or similar to magnetic force (between two magnets) or coulomb force (between two charged object)?
Q 46.
Calculate the force of gravitation between the earth and the Sun, given that the mass of the earth = 6 × 10
24 kg and of the Sun = 2 × 10
30 kg. The average distance between the two is 1.5 × 10
11 m.
Q 47.
The Earth attracts an apple. Does the apple also attract the Earth? If it does, why does the Earth not move towards the apple?
Q 48.
How does value of 'g' vary on the earth? What are the factors responsible for this?
Q 49.
What happens to 'g' experienced by a body when it moves up the earth's surface?
Q 50.
At what height above the surface of the earth, the value of 'g' becomes 64% of its value at the surface of the earth. Take radius of the earth = 6400 km.
