Question:
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 ?
Answer:
(i) The two velocities are equal in accordance with the principle of conservation of energy.During the upward journey,kinetic energy of the body is converted into its potential energy.And during the downward journey of the body,potential energy is converted back into the same kinetic energy.Of course, we assume that there are no stray losses of energy.
(ii) Yes, time taken to fall to ground from maximum height = time taken to go from ground to the maximum height,
(iii) From this brief study, we learn that output can at the most be equal to input,i.e., the degree of our success is always commensurate with our efforts.We reap what we harvest.The degree of sweetness is determined by the amount of sugar we put in.
Gravitation
Q 1.
Fill in the blanks :
Universal gravitational constant G = _____________.
Q 2.
In what direction does the buoyant force on an object immersed in a liquid act?
Q 3.
The volume of 50 g of a substance is 20 cm
3. If the density of water is 1 g cm
-3, will the substance float or sink?
Q 4.
What do you mean by free fall ?
Q 5.
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 6.
What is the SI unit of weight ?
Q 7.
What is the relation between g and G ?
Q 8.
Explain what is meant by ‘free fall’and acceleration due to gravity.
Q 9.
On earth,value of G =
.What is its value on moon,where g is nearly
th that of earth ?
Q 10.
Fill in the blanks :
Geocentric model i.e. the Earth is the orbital centre of all celestial bodies was proposed by _____.
Q 11.
Fill in the blanks :
The force which keeps the object moving in a circular path is called _____ force. It always acts towards the _____.
Q 12.
Fill in the blanks :
Kepler's Law of ______ states that a line that connects a planet to the Sun sweeps out equal ______ in the plane of the planet's orbit in _____time intervals.
Q 13.
Fill in the blanks :
The value of Universal Gravitation constant (G) is ________ Nm
2kgs
-2.
Q 14.
Fill in the blanks :
The mass of the earth is ________ kg.
Q 15.
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 16.
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 17.
Fill in the blanks :
The value of
g on the earth's surface is ______.
Q 18.
Fill in the blanks :
The value of
g at poles is ______ (lower/higher) than its value at the equator.
Q 19.
Fill in the blanks :
The value of
g ________ (increases/decreases) as we go upwards from the earth's surface.
Q 20.
Fill in the blanks :
The value of
g ________ (increases/decreases) as we go downwards from the earth's surface.
Q 21.
Fill in the blanks :
The SI unit of weight is _____.
Q 22.
Fill in the blanks :
Weight of an object is the product of ______ and ________.
Q 23.
What was geocentric model? Who proposed this theory?
Q 24.
State the universal law of gravitation.
Q 25.
What is the importance of Universal Law of Gravitation?
OR
Q: State any one phenomena related to the Universal Law of Gravitation.
Q 26.
Who measured the value of G first time, experimentally?
Q 27.
What is the gravitational force between the Earth and a body called? In which direction does it occur?
Q 28.
An object moves in a circular motion due to centripetal force, acting towards the center. The moon also rotates around the earth? Does centripetal force acts on it? Why does the moon not fall on the earth?
OR
Q:If the moon attracts the earth, why does the earth not move towards the moon?
Q 29.
How gravitational force is different from or similar to magnetic force (between two magnets) or coulomb force (between two charged object)?
Q 30.
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 31.
How is gravitational force of attraction between two bodies affected if(i) Mass of both bodies is doubled.(ii) Distance between them is halved.
Q 32.
Does the force of attraction between two objects depend on the properties of intervening medium?
Q 33.
Does Law of gravitation obey Newton's third law of motion?
Q 34.
(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 35.
How does value of 'g' vary on the earth? What are the factors responsible for this?
Q 36.
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.
Q 37.
Why is the weight of an object on the moon 1/6th its weight on the earth?
Q 39.
Mass of an object is 10 kg. What is its weight on the Earth? (g = 9.8 m/s
2.)
Q 40.
What are the differences between the mass of an object and its weight?
Q 41.
Amit buys few grams of gold at the poles as per the instruction of one of his friends. He hands over the same when he meets him at the equator. Will the friend agree with the weight of gold bought? If not, why? [Hint: The value of g is greater at the poles than at the equator].
Q 42.
Gravitational force on the surface of the moon is only 1/6th as strong as gravitational force on the Earth. What is the weight in newtons of a 10 kg object on the moon and on the Earth? What is the value of 'g' at the surface of the moon?
Q 43.
Write the standard equations in the form when an object is dropped from a height?
Q 44.
Is acceleration due to gravity a vector or a scalar? Write its S.I. unit.
Q 45.
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 46.
A stone is thrown vertically upward with an initial velocity of 40 m/s. Taking g = 10 m/s
2, find the maximum height reached by the stone. What is the net displacement and the total distance covered by the stone?
Q 47.
A ball is thrown with some velocity 'u' m/s. Show that under free fall, it will fall the ground with same velocity.
Q 48.
Two stones A and B are dropped from a multistoried building. A is dropped from 100 m and after some time B is dropped from 50 m height. Both of them reach the earth at the same time. Will they have equal velocity while reaching the ground ? Calculate and find out the answer (take g =10 m/s
2).
Q 49.
When a ball is thrown upwards, it falls back to the ground. Name the force which makes it fall.
Q 50.
Name the scientist who identified the relation about force of gravitation. Name the law.
