Question:
Take a piece of thread.Tie a small piece of stone to one end of the thread. Hold the other end of the thread in hand and whirl it round.Note the motion of the stone.If the thread breaks suddenly,the stone flies off along tangent to the circle at that instant.
Read the above passage and answer the following questions:
(i) Which force Is whirling the stone ? Who is providing this force ?
(ii) Why does the stone fly off along the tangent to the circle at that instant ?
(iii) What values of life do you learn from this ?
Answer:
(i) The force whirling the stone is the centripetal force acting on the stone.This force is being provided by our hand whirling the stone.
(ii) When the thread breaks, centripetal force is no longer provided. Therefore, inertia of direction takes the stone along the straight line path ;which is along tangent to the circle at that instant
(iii) From these observations,we learn that to keep our children on track,motivation has to be continuous.This applies equally to our lives too.The moment our efforts and motivation cease,our life/children are likely to go off the track.
Gravitation
Q 1.
State Kepler’s Laws of planetary motion. How did Newton guess inverse square law ?
Q 2.
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 3.
Calculate the value of acceleration due to gravity on Moon. Given mass of Moon =
kg, radius of Moon = 1740 km
Q 4.
Why do sewing needles and all pins have a sharp pointed tip?
Q 5.
What is the value of ‘g’ at the centre of Earth ?
Q 6.
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 7.
Which force is responsible for tides in the ocean at night ?
Q 8.
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 9.
Fill in the blanks :
Every object in the universe ________ other bodies.
Q 10.
Can you calculate density of Earth from Newton’s law of gravitation ?
Q 11.
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 12.
What do we call the gravitational force between the Earth and an object ?
Q 13.
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 14.
What do you mean by acceleration due to gravity ?
Q 15.
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 16.
Fill in the blanks :
________ of an object is the force of gravity acting on it.
Q 17.
What is the importance of universal law of gravitation ?
Q 18.
Who measured the value of G first time, experimentally?
Q 19.
What is value of ‘g’ on Earth ?
Q 20.
State and explain universal law of gravitation given by Newton.What is the importance of this law
Q 21.
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 22.
Mass of an object is 10 kg. What is its weight on the Earth? (g = 9.8 m/s
2.)
Q 23.
Distinguish between mass and weight.
Q 24.
What happens to 'g' experienced by a body when it moves up the earth's surface?
Q 25.
Fill in the blanks :
Universal gravitational constant G = _____________.
Q 26.
A body is projected upwards. What is its velocity at maximum height
Q 28.
Why will a sheet of paper fall slower than one that is crumpled into a ball?
Q 29.
Why does a block of plastic released under water come up to the surface of the water?
Q 30.
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 31.
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 32.
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 33.
Fill in the blanks :
The value of
g ________ (increases/decreases) as we go downwards from the earth's surface.
Q 34.
Does the force of attraction between two objects depend on the properties of intervening medium?
Q 35.
Is weight a scalar quantity?
Q 36.
The weight of a man is 690N which contains 5.3 x 10
-3 m
3 of blood. Find (a) blood's weight. Take density of blood is 1060 kg/m
3 (b) express it as a percentage of body weight.
Q 37.
What do you mean by Thrust or Buoyant force?
Q 38.
Write the formula to find the magnitude of the gravitational force between the Earth and an object on the surface of the Earth.
Q 39.
Why is the weight of an object on the Moon (l/6)th its weight on the Earth ?
Q 40.
Why will a sheet of paper fall slower than one that is crumpled into a ball ?
Q 41.
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 42.
A stone is allowed to fall from the top of a tower 100 m high and at the same time another stone is projected vertically upwards from the ground with a velocity of 25 m/s. Calculate when and where the two stones will meet
Q 43.
Does value of ‘g’ vary from place to place on Earth ?
Q 44.
A body is just dropped from a height What is its initial velocity ?
Q 45.
What is the SI unit of weight ?
Q 46.
In free fall, will heavier objects accelerate more than light ones ?
Q 47.
Can a body have mass but no weight ?
Q 48.
Can a body have weight but no mass ?
Q 49.
Can you calculate mass of Earth from Newton’s law of gravitation ?
Q 50.
A body weighs 10 kg on the surface of earth.What would be its mass and weight at the centre of earth ?
