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.
Is mass a scalar quantity?
Q 2.
Explain what is meant by ‘free fall’and acceleration due to gravity.
Q 3.
Comment on application of Newton’s third law of motion to gravitation.Illustrate by examples.
Q 4.
Fill in the blanks :
The force of gravity _________ with altitude. It also varies on the surface of the earth, _________ from poles to the equator.
Q 5.
What are the factors the buoyant force depends on?
Q 6.
What is the SI unit of weight ?
Q 7.
How are gravitation and gravity related ?
Q 8.
Can you calculate mass of Earth from Newton’s law of gravitation ?
Q 9.
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 11.
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 12.
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 13.
If the distance of Earth from the Sun were half the present value,how many days will make one year ?
Q 14.
A stone falling towards Earth also attracts the Earth with the same force.Is it true ?
Q 15.
Does value of ‘g’ vary from place to place on Earth ?
Q 16.
Distinguish between mass and weight.
Q 17.
Who measured the value of G first time, experimentally?
Q 18.
What are the differences between the mass of an object and its weight?
Q 19.
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 20.
Fill in the blanks :
It is the ____________ of the earth, which holds our atmosphere in place.
Q 21.
The pressure at the bottom of a filled glass (density = 1000 kg/m
3) of water is P. The water is taken out and the glass is filled with kerosene oil (density = 817.5 kg/m
3). Now the pressure at the bottom will be a. same as P b. smaller than P c. larger than P d. cannot be determined.
Q 22.
Why do sewing needles and all pins have a sharp pointed tip?
Q 23.
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 24.
How does the force of gravitation between two objects change when the distance between them is reduced to half ?
Q 25.
Who gave three laws of planetary motion ?
Q 26.
What is the value of ‘g’ at the centre of Earth ?
Q 27.
State Kepler’s Laws of planetary motion.
Q 28.
On earth,value of G =
.What is its value on moon,where g is nearly
th that of earth ?
Q 29.
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 30.
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 32.
How does value of 'g' vary on the earth? What are the factors responsible for this?
Q 33.
Why is the weight of an object on the moon 1/6th its weight on the earth?
Q 34.
As you climb up a mountain, your ears “pop” because of the changes in atmospheric pressure. In which direction, outward or inward, does your eardrum move when you climb up?
Q 35.
An object is thrown vertically upwards and rises to a height of 10 m. Calculate (i) the velocity with which the object was thrown upwards and (ii) the time taken by the object to reach the highest point.
Q 36.
What is the value of G (i) on Earth (ii) on Moon ?
Q 37.
Which force revolves Moon around Earth ?
Q 38.
Which force accelerates a body in free fall ?
Q 39.
What is the usual shape of orbits of planets around the Sun ?
Q 40.
Does Newton’s third law of motion apply to gravitational force ?
Q 41.
Can you calculate density of Earth from Newton’s law of gravitation ?
Q 42.
Compare gravitational force between light objects and heavy objects.
Q 43.
Fill in the blanks :
Heliocentric model was proposed by ______.
Q 44.
Fill in the blanks :
The force which keeps the object moving in a circular path is called _____ force. It always acts towards the _____.
Q 45.
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 46.
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 47.
Fill in the blanks :
Acceleration due to gravity (g) is _______ (dependent/independent) of mass.
Q 48.
Fill in the blanks :
The value of
g on the earth's surface is ______.
Q 49.
Fill in the blanks :
The value of
g at poles is ______ (lower/higher) than its value at the equator.
Q 50.
State the universal law of gravitation.
