Question:
Explain what is meant by ‘free fall’and acceleration due to gravity.
Answer:
Refer to Art 3.11, Page 159.
Gravitation
Q 1.
Is mass a scalar quantity?
Q 3.
How are gravitation and gravity related ?
Q 4.
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 6.
Who gave three laws of planetary motion ?
Q 7.
Fill in the blanks :
Heliocentric model was proposed by ______.
Q 8.
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 9.
If the distance of Earth from the Sun were half the present value,how many days will make one year ?
Q 10.
Compare gravitational force between light objects and heavy objects.
Q 11.
What are the differences between the mass of an object and its weight?
Q 12.
Is acceleration due to gravity a vector or a scalar? Write its S.I. unit.
Q 13.
Fill in the blanks :
The SI unit of weight is _______.
Q 14.
Fill in the blanks :
It is the ____________ of the earth, which holds our atmosphere in place.
Q 15.
The following figure shows four containers containing a liquid at the same height. Rank them according to the pressure exerted by the liquid on the bottom of the containers in ascending order.
a. 1, 2, 3, 4 b. 4. 3, 1, 2 c. 3, 4, 1, 2 d. same pressure in each case.
Q 16.
Why do sewing needles and all pins have a sharp pointed tip?
Q 17.
What do we call the gravitational force between the Earth and an object ?
Q 18.
The distance between two objects is doubled. What happens to gravitational force between them
Q 19.
Does Newton’s third law of motion apply to gravitational force ?
Q 20.
Then why Is the Earth not seen moving towards the stone ?
Q 21.
What is value of ‘g’ on Earth ?
Q 22.
Explain what is meant by ‘free fall’and acceleration due to gravity.
Q 23.
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 24.
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 25.
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 26.
How does the force of gravitation between two objects change when the distance between them is reduced to half ?
Q 27.
A stone is thrown vertically upward with an initial velocity of 40 m/s.Taking g =
,find the maximum height reached by the stone.What is the net displacement and the total distance covered by the stone ?
Q 28.
What is the source of centripetal force that a planet requires to revolve around the Sun ? On what factors does that force depend ?
Q 29.
Does value of ‘g’ vary from place to place on Earth ?
Q 30.
Where is ‘g' maximum, on the surface of Earth, above the surface or below the surface of Earth ?
Q 31.
Can you calculate mass of Earth from Newton’s law of gravitation ?
Q 32.
Comment on application of Newton’s third law of motion to gravitation.Illustrate by examples.
Q 33.
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 34.
Fill in the blanks :
The value of
g at poles is ______ (lower/higher) than its value at the equator.
Q 35.
What was geocentric model? Who proposed this theory?
Q 36.
Define 'g' or acceleration due to gravity? Does it depend on the mass of the body (near the surface of the earth)experiencing 'g'?
Q 37.
How does value of 'g' vary on the earth? What are the factors responsible for this?
Q 38.
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 39.
Fill in the blanks :
The gravitational force between the earth and the object is generally called ____________.
Q 40.
Why will a sheet of paper fall slower than one that is crumpled into a ball?
Q 41.
You find your mass to be 42 kg on a weighing machine. Is your mass more or less than 42 kg?
Q 42.
A cuboid room has dimensions 50m x 15m x 3.5m. What is the mass of the air enclosed in the room if the density of air = 1.30 kg/m
3.
Q 43.
Relative density of silver is 10.8. If the density of water is 10
3kg/m
3, find density of silver.
Q 44.
The mass of Sun is
kg and mass of Earth is
kg. If the distance between the centres of Sun and Earth is
km,calculate the force of gravitation between them.
Q 45.
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 46.
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 47.
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 48.
State the universal law of gravitation.
Q 49.
What do you mean by acceleration due to gravity ?
Q 50.
What are the differences between the mass of an object and its weight ?
