Monday 11 June 2018

GRAVITATION 9


Practice Paper 
Subject Physics (2020)
CH –10   GRAVITATION 

Class IX 

I. Very short answer type questions:
  1. Write one difference between gravitation and gravity.
  2. How is acceleration due to the gravity of falling body related to its mass?
  3. Why G is called universal constant?
  4. Define mass and weight of an object.
  5. Can the mass of an object be zero?
  6. What do you understand by the gravitational force of earth?
  7. How does acceleration due to gravity change with the shape of the earth?
  8. Is the value of G dependent on the medium present between the two bodies?
  9. At what place on the earth surface is the weight of a body be maximum and minimum?
  10. If the mass of a body is 8 Kg and weight is 12 N then what will be its mass and weight in the moon? 
  11. State the factors on which acceleration due to gravity 'g' and 'G' depends
  12. On what factors does the weight of a body depends?
  13. How does the weight of a rocket change as it moves from earth to moon?
  14. What is the relation between the weight of an object on the moon and on the earth?
II. Short answer type questions
  1. Give reasons for the following:
    (a) A sheet of paper falls slower than when it is crumpled into a ball.
    (b) What is meant by the statement that acceleration due to gravity is 9.8 m/s?
  2. What is meant by free fall? A stone and a small coin are dropped from the same height and the same time, which of the two will touch the ground first? 
  3. Write the units of the following:
    (a) Gravitational constant G
    (b) Mass
    (c) Weight.
  4. Explain what happens to the force between two objects if:
    (a) The mass of one object is doubled?
    (b) The distance between the two objects is tripled?
  5. What is the importance of the universal law of Gravitation? Or State any four natural phenomena explained by the universal law of Gravitation.
  6. How does the force of gravity between two objects change when the distance between them is reduce to half?
  7. Stone and the earth attract each other with an equal and opposite force. Why then we see only the stone falling towards the earth but not the earth rising towards the stone? 
  8. Write three differences between 'g'(gravitational acceleration) and 'G'(gravitational constant).
  9. Give the relation between mass and weight. What kind of quantity is the weight?
  10. A man of mass 60 Kg is standing on the floor holding a stone weighing 40N. What is the force with which the floor is pushing him up?
  11. A ball is thrown vertically upwards with a velocity of 49 m/s. Calculate:
    (a) The maximum height to which it reaches.
    (b) The total time it takes to return to the earth's surface.
  12. A body of weight 600N rests on a lift. If the lift begins to fall freely under the gravity, what is the force with which the body presses on the floor? 
  13. A sphere of mass 40 kg is attracted by another sphere of mass 80 kg. by a force of 2.5 x10-6 N and when their centers are 300 mm apart Find the value of G.
  14.  A ball is thrown upwards from the ground at a tower with a speed of 20 meters per second. There is a window in the tower at a height of 15 m from the ground. How many times and when will the ball pass a window?
  15.  (a) Seema byes a few grams of gold at the pole as per the instruction of one of her friends. She hands over the same when she meets her friend at the equator. Will the friend agree with the weight of gold bought? If not why?
    (b) If the moon attracts the earth, why does the earth not move towards the moon?
  16. 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. 
III. Long answer type questions:
  1. Write the name of the scientist:
    (a) Who discovered that force is the cause of motion?
    (b) Who formulated the universal law of gravitation?
    (c) Who found out the value of gravitational constant 'G’.
  2. What happens to the magnitude of the force of gravitation between two objects if:
    (a) Mass of one of the objects is tripled?
    (b) The distance between the objects is doubled?
    (c) The mass of both objects is doubled.
  3. (I)Write the name of the scientist:
    (a) Who discovered that force is the cause of motion?
    (b) Who formulated the universal law of gravitation?
    (c) Who found out the value of gravitational constant 'G’.
    (II) (a)Explain why the value of 'g' is greater at poles than the equator.
    (b) Why does a body reach the ground quicker at poles than equator when dropped from the same height?
  4. Derive an expression for acceleration due to gravity in terms of mass M of earth and radius R.
  5. A stone is dropped from the edge of the roof. It passes a window 2m high in 0.1sec.How far is the roof above the window? 
  6. State the Universal law of Gravitation? Derive an expression for gravitational force between two bodies.
  7. A stone is dropped from a height of 50 m on earth. At the same time, another stone is thrown vertically upwards from the ground with a velocity of 50m/s. At what height from the ground will the two stones meet (g = -10).
  8. A ball is thrown vertically upwards. The speed of the ball was 10m/s when it had reached one half of its maximum height.
    (a) How high does the ball rise? 
    (b) Find the velocity and acceleration 1sec. after it is thrown.
  9. If the mass of one the object is doubled and the mass of other remains the same and if the distance between them is halved then how does the gravitational force change?
  10. The radius of the earth is about 6370 Km. An object of mass 30 Kg is taken to a height of 230km above the surface of the earth.
    (a) What is the mass of the body?
    (b) What is the acceleration due to gravity at this height?
    (c) What is the weight of the body at this height?
  11. What is the magnitude of the gravitational force exerted by a 15Kg mass on a 25 Kg mass separated by a distance of 25 cm? What is the acceleration produced on each mass?
  12. A boy on a cliff 49 m high, drops a stone, one second later, he throws another stone vertically downwards. The two stones hit the ground at the same time. What was the velocity with which the second stone was thrown?
  13. A ball is thrown vertically upward and it returns after 6 sec. Find:
    (a) The velocity with which it was thrown up.
    (b) The max.height it reaches.
    (c) Its position after 4 sec.
  14. (a)A ball is dropped from the roof of a building, it takes 10 seconds to reach the ground to find the height of the building.
     (b) A stone is released from the top of a tower of height 19.6 m. Calculate its velocity just before touching the ground.
  15. (a) Determine the magnitude of the gravitational force between a planet of mass 6 x 1026 .kg and a 1 kg object on its surface. Let the radius of the planet be 6 x 106m. G = 6.67 x 10-11Nm2kg.
    (b) To estimate the height of the bridge over a river, a stone is dropped freely in the river from the bridge. The stone takes 2 sec. to reach the water surface in the river.  Calculate the height of the bridge from the water level.
  16. (a) An astronaut carried a pot containing soil waiting for 60 Newton from the earth to the surface of the motion moon he kept it there and just before return journey from Moon to Earth he waited for the soil there on the surface of the moon and found that it was only 10 Newton where did the rest of soil go and how much mass of soil has lost? 
    (b) Find the weight of an 80 kg man on the surface of the moon? What should be his mass on the earth and on the Moon?
    (c)An object of mass 8 units weight 300 Newton on the surface of earth what would be its mass and weight on the surface of the moon?
  17.  (a)  Find the weight of an 80 kg man on the surface of the moon? What should be his mass on the earth and on the Moon?
    (b) An object of mass 8 units weight 300 Newton on the surface of earth what would be its mass and weight on the surface of the moon?]
  18. There are 2 planets A and B masses m1 and m2 respectively. They revolve around the sun in a circular orbit. The orbital radius of A from the sun is twice that of orbital radius of B. The mass of A is twice that of the mass of B.Compare the forces of gravitation between A to Sun and B to Sun.
  19. (a) Calculate the force of gravitation between two objects of mass 50 kg and 120 kg. Kept at a distance of 10 m from one another.
    (a) A stone is dropped from a height of 10 m on an unknown planet having g = 20 m/s2.  Calculate the speed of the stone when it hits the surface of the planet. Also, calculate the time it takes to fall through this height.
  20. A ball is thrown upward from the ground at a tower with a speed of 20 m/s There is a window in the tower at the height of 15 m from the ground. How many times and when will the ball pass the window?
  21. A sphere of mass 40 kg is attracted by another sphere of mass 80 kg by a force of 2.5 x10 -6 N when their centers are 300 mm apart. Find the value of G.
  22. A ball is thrown vertically up returns to the thrower after 6s. Find
    (a) The velocity with which it was thrown up.
    (b) The maximum height it reaches its position after 4 seconds.
  23. Determine the magnitude of the gravitational force between a planet of mass 6 x 1024 kg and a 1kg object on its surface. Let the radius of the planet be 6 x106 m. G= 6.67 x10-11 N m2 kg-2
  24. To estimate the height of a bridge over the river, a stone is dropped freely in the river from the bridge. The stone takes 2s to touch the water surface in the river. Calculate the height of the bridge from the water level.
FLOATATION
  1. State Archimedes Principle?
  2. What makes a body to float or sink in a liquid? 
  3. Define density and relative density? Calculate the pressure at a depth of 50 m below the surface of the sea. The density of seawater is 1024 Kg/m3.
  4. What are the fluids? What are the factors on which the upward pressure at a point on a fluid depends?
  5. Define Pressure? How is thrust different from Pressure? 
  6. Write the units of pressure and Relative density.
  7. What is the S.I unit of pressure?
  8. Give a mathematical proof of the Archimedes principle? 
  9. What is the upthrust experienced by a balloon of volume 120 m3 filled with hydrogen? The density of air = 1.140 Kg/m3 and density of hydrogen =0.081 Kg/m3 at room temperature. What is the maximum weight this balloon can lift?
  10. What is the upthrust experienced by a cube of edge – length 5cm made of iron when completely immersed in ethanol of density 0.8 g/cm3.
  11. A cylindrical block of wood of height 4.2 m and mass 100 Kg floats vertically in the water. The relative density of wood is 0.8.
    (a) What height of the block will be seen above the water?
    (b) If the block of the lead of mass 10kg is placed, what height of the block will be seen above water?
  12. Give one reason why a block of plastic when released underwater comes up to the surface of the water. 
  13. When we jump into a swimming pool we feel lighter. Why?
  14. What is meant by upthrust?
  15. State two factors on which the upthrust force depends?
  16. What are the two forces act on the object in the vertically opposite direction when the object is immersed into the liquid?
  17. Define the relative density of a substance?
  18. What are the fluids?
  19. In what direction does the buoyant force act on an object immersed in a liquid?
  20. Why does object float or sink when placed on the surface of the liquid?
  21. An iron nail floats on mercury but sinks in water. Why?  
  22. A woman walking in high hills can damage a hardwood floor by making small dimples on the floor since her weight is concentrated on such a small area. If the women weigh 60N and tip of the high heel is 2 cm2, what will be the pressure exerted on the floor by her high heel? 
  23. A cube of side 5 cm is immersed in water and then in the saturated salt solution. In which case will it experience a greater buoyant force? If each side of the cube is reduced to 4 cm and then immersed in water compare force experienced by the cube, as compared to the first case. Give reasons for each case. 
  24. The volume of 50 gm of a substance is 20cm3. If the density of the water is 1 g cm-3, will the substance float or sink in water? Justify your answer.
  25. The pressure exerted by the weight of a cubical block of side 4 cm on the surface is 10 Pascal. Calculate the weight of the block.
  26. Give reasons:(i) Why do buildings have a wide foundation? (i)Tractors have broad tires.
  27. Out of the positions given below, in which case do you apply more pressure on loose sand and why?
    (i) While you are standing
    (ii) while you lie down. Why does an army tank rest upon a continuous chain?
  28. A metallic block of 6 kg is dropped into a water tank. The volume of the block is given to be 3 x 10-3m3 and density of water is 103 kg/m3. Find (a) Buoyant force on the block, (b) density of the metallic block.
  29. Why is a bucket of water lighter when in water than when it is taken out of water?
  30. A ball of mass 4 kg and density 4000 kg m3 is completely immersed in water of density 103 kg m-3. Find the buoyant force on the ball.(Given g = 10 ms-2).
  31. (i) An object of volume V is immersed in a liquid of density p. Calculate the magnitude of a buoyant force acting on the object due to the liquid?
    (ii) Mention the direction of buoyant force.
  32. Why is it difficult to hold a bag having a strap made of a thin and strong string?
  33. What happens when :
    (i) The buoyant force exerted by the fluid is greater than the weight of the body
    (ii) Buoyant exerted by the fluid is equal to the weight of the body?
  34. State Archimedes’ Principle. Give two applications of this principle.
  35. A sphere of iron and another of wood having the same radius are held underwater. Which of these experiences a greater buoyant force?
  36. (i)The density of water is 103 kg/m3 If the relative density of Al is 2.7, calculate the density of Al in g/cm3.
    (ii) If the relative density of Ag is 10.8, calculate the density of At in g/cm3.
  37. The dimension of the wooden block is 2 m x 25 m x 0.10 m. If the relative density of wood is 0.6, calculate the mass of the block in kg. Density of the water = 103 kg/m3.
  38. (i) Why are railway tracks laid on large-sized concrete sleepers?
    (ii) While drawing water from a well, the bucket of water appears to be heavier as it comes out of the water.
  39. (i) Name the instrument which is used to determine the density of a liquid.
    (ii) The volume of a 250 gm sealed packed is 500 cm3. Will the packet float or sink in water, if the density of water is 1 g/cm3.
  40. The volume of a 500 gm sealed packed is 350 cm3. Its density is 1.4 g/cm3. What will be the mass of the water displaced by this packet? (Density of water = 1 g/cm3).
  41. What would be the apparent weight of an iron block of size 5 cm x 5 cm x 5 cm when it is completely immersed in water? (Density of iron = 7.8 g/c.c).
  42. Define pressure and state its S.I unit. The dimensions of a metallic cuboid are 30 cm x 20 cm x 15 cm and its mass is 30 kg. If the acceleration due to gravity is 10 m/s2.Calculate the pressure exerted by the cuboid when it is resting on the face having sides 20 cm x 15 cm on a table. 
  43. Define thrust and state its S.I unit.
  44. An iron cube of side 10 cm is kept on a horizon table. If the density of iron is 8000 kg/m3. Find the pressure on the portion of the table where the cube is kept. (g = 10 m/s2. ) 
  45. A cubical block of side 2 cm is lying on a table. If the density of the material of the cube is 10.000 kg/m3, find the pressure exerted by the block on the table. (g = 10 m/s2. ) 
  46. Lactometers are used to determine the purity of a sample of milk. State the principle on which this instrument is based on.
  47. (i) Define density. 
    (ii) State unit of density in S.I. 
    (iii) How can we identify whether the substance is pure or not by knowing its density?
  48. How the Archimedes principle is used to design ships and submarines.
  49. Mention the uses of Lactometer and Hydrometer.
  50. Deduce the formula for the buoyant force acting on a fully immersed object in terms of its volume, the density of liquid and acceleration due to gravity.
  51. The weight of the balloon and gas inside it is 12N. The volume of the balloon is 1200 m^3. The density of air is 1.26 Kg/m^3. 
    Calculate (a) the weight it can lift(b) the acceleration as it rises.

NCERT QUESTIONS:
  1. State the universal law of gravitation. 
  2. Write the formula to find the magnitude of the gravitational force between the earth and an object on the surface of the earth.
  3. What do you mean by free fall? 
  4. What do you mean by acceleration Q due to gravity?
  5. What are the differences between the mass of an object and its weight? 
  6. Why is the weight of an object on the moon 16th its weight on the earth?
  7. Why is it difficult to hold a school bag having a strap made of a thin and strong string? 
  8. What do you mean by buoyancy? 
  9. Why does an object float or sink when placed on the surface of the water?
  10. You find your mass to be 42 kg on a weighing machine. Is your mass more or less than 42 kg?
  11. How does the force of gravitation between two objects change when the distance between them is reduced to half? 
  12. Gravitational force acts on all objects in proportion to their masses. Why then, a heavy object does not fall faster than a light object? 
  13. What is the magnitude of the gravitational force between the earth and a 1 kg object on its surface? (Mass of the earth is 6 × 1024 kg and the radius of the earth is 6.4 × 106 m.) 
  14. The earth and the moon are attracted to each other by gravitational force. Does the earth attract the moon with a force that is greater or smaller or the same as the force with which the moon attracts the earth? Why? 
  15. If the moon attracts the earth, why does the earth not move towards the moon?
  16. What happens to the force between two objects, if (i) the mass of one object is doubled? (ii) the distance between the objects is doubled and tripled? (iii) the masses of both objects are doubled? 
  17. What is the importance of the universal law of gravitation? 
  18. What is the acceleration of free fall? 
  19. What do we call the gravitational force between the earth and an object? 
  20. Amit buys few grams of gold at the poles as per the instruction of one of his friends. He hands over the same when he meets him at the equator. Will the friend agree with the weight of gold bought? If not, why? [Hint: The value of g is greater at the poles than at the equator.] 
  21. Why will a sheet of paper fall slower than one that is crumpled into a ball? 
  22. The gravitational force on the surface of the moon is only 16 as strong as gravitational force on the earth. What is the weight in newton’s of a 10 kg object on the moon and on the earth? 
  23. A ball is thrown vertically upwards with a velocity of 49 m/s. Calculate (i) the maximum height to which it rises, (ii) the total time it takes to return to the surface of the earth. 
  24. A stone is released from the top of a tower of height 19.6 m. Calculate its final velocity. 
  25. A stone is thrown vertically upward with an initial velocity of 40 m/s. Taking g = 10 m/s2, find the maximum height reached by the stone. What is the net displacement and the total distance covered by the stone? 
  26. Calculate the force of gravitation between the earth and the Sun, given that the mass of the earth = 6 × 1024 kg and of the Sun = 2 × 1030 kg. The average distance between the two is 1.5 × 1011 m. 
  27. 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. 
  28. A ball thrown up vertically returns to the thrower after 6 s.
    Find (a) the velocity with which it was thrown up, (b) the maximum height it reaches, and (c) its position after 4 s
  29. In what direction does the buoyant force on an object immersed in a liquid act? 
  30. Why a block of plastic does release underwater come up to the surface of the water? 
  31. The volume of 50 g of a substance is 20 cm3. If the density of water is 1 g cm–3, will the substance float or sink? 
  32. The volume of a 500 g sealed packet is 350 cm3. Will the packet float or sink in water if the density of water is 1g cm–3? What will be the mass of the water displaced by this packet?
  33. You have a bag of cotton and an iron bar, each indicating a mass of 100 kg when measured on a weighing machine. In reality, one is heavier than the others. Can you say which one is heavier and why?




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