Question:
State Kepler’s Laws of planetary motion. How did Newton guess inverse square law ?
Answer:
Refer to Art 3.8 and 3.9, Pages 146 to 147.
Gravitation
Q 1.
State Kepler’s Laws of planetary motion. How did Newton guess inverse square law ?
Q 2.
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 3.
What do we call the gravitational force between the Earth and an object ?
Q 4.
Can you calculate density of Earth from Newton’s law of gravitation ?
Q 5.
What do you mean by acceleration due to gravity ?
Q 6.
Suppose a planet exists whose mass and radius both,are half those of Earth.Calculate the acceleration due to gravity on the surface of this planet.
Q 7.
What is the value of ‘g’ at the centre of Earth ?
Q 8.
Why do sewing needles and all pins have a sharp pointed tip?
Q 9.
Fill in the blanks :
Every object in the universe ________ other bodies.
Q 10.
A particle is dropped from a tower 180 m high.How long does it take to reach the ground ? What is the velocity when it touches the ground ? Take g =
Q 11.
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 12.
Calculate the value of acceleration due to gravity on Moon. Given mass of Moon =
kg, radius of Moon = 1740 km
Q 13.
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 14.
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 15.
Fill in the blanks :
________ of an object is the force of gravity acting on it.
Q 16.
Fill in the blanks :
Weight of an object is the product of ______ and ________.
Q 17.
Fill in the blanks :
The gravitational force between the earth and the object is generally called ____________.
Q 18.
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 19.
Is weight a scalar quantity?
Q 20.
A ball is thrown up with a speed of 15 m/s.How high will it go before it begins to fall ? Take g=
Q 21.
Which force revolves Moon around Earth ?
Q 22.
Who explained the motion of planets around the Sun ?
Q 23.
Can a body have weight but no mass ?
Q 24.
Fill in the blanks :
The value of
g ________ (increases/decreases) as we go downwards from the earth's surface.
Q 25.
How does value of 'g' vary on the earth? What are the factors responsible for this?
Q 26.
Fill in the blanks :
The average acceleration of free fall on the surface of earth is ______ .
Q 27.
The mass of Earth is
kg and that of moon is
kg. If the distance between the Earth and the Moon is
km, calculate the force exerted by Earth on the Moon. Given G =
.
Q 28.
To estimate the height of a bridge over a river,a stone is dropped freely on the river from the bridge.The stone takes 2 s to touch the water surface in the river.Calculate the height of the bridge from the water level.Take g = 9.8
.
Q 29.
Where is ‘g' maximum, on the surface of Earth, above the surface or below the surface of Earth ?
Q 30.
Distinguish between gravitation and gravity.
Q 31.
Fill in the blanks :
The force of attraction between two objects is ______ proportional to the product of their masses and _____ proportional to the square of a distance between them.
Q 32.
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 33.
Write the standard equations of motion when an object is thrown upwards with some initial velocity?
Q 34.
A ball is thrown upwards from the ground of a tower with a speed of 20 m/s. There is a window in the tower at the height of 15m from ground. How many times and when will the ball pass the window? (g = 10 m/s
2)
Q 35.
Fill in the blanks :
It is the ____________ of the earth, which holds our atmosphere in place.
Q 36.
Why will a sheet of paper fall slower than one that is crumpled into a ball?
Q 37.
Calculate the force of gravitation between two objects of masses 80 kg and 1200 kg kept at a distance of 10 m from eachother.Given, G =
/
.
Q 38.
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 39.
What is the gravitational acceleration of a spaceship at a distance equal to two Earth’s radius from the centre of the Earth ?
Q 40.
A force of 20 N acts upon a body whose weight is 9.8 N.What is the mass of the body and how much is its acceleration ?
Q 41.
What is the importance of universal law of gravitation ?
Q 42.
Does Newton’s third law of motion apply to gravitational force ?
Q 43.
A stone falling towards Earth also attracts the Earth with the same force.Is it true ?
Q 44.
Define g and G.Establish relation between them.
Q 45.
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 46.
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 47.
Fill in the blanks :
The value of Universal Gravitation constant (G) is ________ Nm
2kgs
-2.
Q 48.
Fill in the blanks :
The value of G was found out by _______ by using a ________.
Q 49.
What was heliocentric theory? Who proposed this?
Q 50.
What are the Kepler Laws that govern the motion of the planets?
