Question:
What was geocentric model? Who proposed this theory?
Answer:
Ptolemy a Greek mathematician and astronomer proposed geocentric model around 125 AD. According to this model, the earth is in the center and sun, other planets and stars move around it.
To explain retrograde motion of planets, he also proposed that those planet also move in small circle. The geocentric theory held valid till 1543 AD when Copernicus proposed heliocentric model.
Gravitation
Q 1.
State Kepler’s Laws of planetary motion. How did Newton guess inverse square law ?
Q 2.
Why do sewing needles and all pins have a sharp pointed tip?
Q 3.
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 4.
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 5.
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 6.
Calculate the value of acceleration due to gravity on Moon. Given mass of Moon =
kg, radius of Moon = 1740 km
Q 7.
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 8.
Fill in the blanks :
Every object in the universe ________ other bodies.
Q 9.
What is the value of ‘g’ at the centre of Earth ?
Q 10.
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 11.
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 12.
What do you mean by acceleration due to gravity ?
Q 13.
State and explain universal law of gravitation given by Newton.What is the importance of this law
Q 14.
Which force is responsible for tides in the ocean at night ?
Q 15.
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 16.
What do we call the gravitational force between the Earth and an object ?
Q 17.
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 18.
Can you calculate density of Earth from Newton’s law of gravitation ?
Q 19.
Fill in the blanks :
________ of an object is the force of gravity acting on it.
Q 20.
Fill in the blanks :
The value of
g at poles is ______ (lower/higher) than its value at the equator.
Q 21.
Who measured the value of G first time, experimentally?
Q 23.
Fill in the blanks :
Heliocentric model was proposed by ______.
Q 24.
Fill in the blanks :
The value of
g on the earth's surface is ______.
Q 25.
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 26.
What is the gravitational acceleration of a spaceship at a distance equal to two Earth’s radius from the centre of the Earth ?
Q 27.
The distance between two objects is doubled. What happens to gravitational force between them
Q 28.
What happens to 'g' experienced by a body when it moves up the earth's surface?
Q 29.
Write the standard equations of motion when an object is thrown upwards with some initial velocity?
Q 30.
Fill in the blanks :
Assuming negligible air drag, if a steel ball and a table tennis ball are dropped from a height of 100 metres, both will reach the ground at ________ time(s). (same/different)
Q 31.
Write the formula to find the magnitude of the gravitational force between the Earth and an object on the surface of the Earth.
Q 32.
Why is the weight of an object on the Moon (l/6)th its weight on the Earth ?
Q 33.
What is the importance of universal law of gravitation ?
Q 34.
Why will a sheet of paper fall slower than one that is crumpled into a ball ?
Q 35.
Does gravitational force between two objects depend on medium between them ?
Q 36.
What is the SI unit of mass ?
Q 37.
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 38.
Fill in the blanks :
Weight of an object is the product of ______ and ________.
Q 39.
What are the Kepler Laws that govern the motion of the planets?
Q 40.
Mass of an object is 10 kg. What is its weight on the Earth? (g = 9.8 m/s
2.)
Q 41.
What are the differences between the mass of an object and its weight?
Q 43.
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 44.
Fill in the blanks :
A body is said to be in _______ when only gravity acts on it.
Q 45.
Fill in the blanks :
Universal gravitational constant G = _____________.
Q 46.
What do you mean by Thrust or Buoyant force?
Q 47.
The volume of a 500 g sealed packet is 350 cm
3. 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 48.
A stone drops from the edge of the roof.It passes a window 2 m high in 0.1 s.How far is the roof above the top of the window
Q 49.
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 50.
A car falls off a ledge and drops to the ground in 0.5 s.Let g =
(for simplifying the calculations).
(i) What is its speed on striking the ground ?
(ii) What is its average speed during 0.5 s ?
(iii) How high is the ledge from the ground ?
