physics - gravitation

Class 9 - Physics


Mass of an object is 10 kg. What is its weight on the Earth? (g = 9.8 m/s2.)

Weight = mass(m) × acceleration due to gravity(g) = mg
W = 10 × 9.8 = 98N

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Questions and Answers

Gravitation - Questions
1. What do you mean by Thrust or Buoyant force?
2. Fill in the blanks :
The value of G was found out by _______ by using a ________.
3. 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?
4. What is free fall?
5. 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 radius of the earth is 6.4 × 106 m).
6. Gravitational force on the surface of the moon is only 1/6th as strong as gravitational force on the Earth. What is the weight in newtons of a 10 kg object on the moon and on the Earth? What is the value of 'g' at the surface of the moon?
7. 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.
8. 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.
9. Define thrust.
10. Why does one feel giddy while moving on a merry go round ?
11. Fill in the blanks :
Every object in the universe ________ other bodies.
12. Fill in the blanks :
________ of an object is the force of gravity acting on it.
13. Fill in the blanks :
The SI unit of mass is ______.
14. Fill in the blanks :
All other variables remaining constant, the force of gravitation is ________ proportional to the square of distance between the two objects.
15. 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)
16. The weight of a man is 690N which contains 5.3 x 10-3 m3 of blood. Find (a) blood's weight. Take density of blood is 1060 kg/m3 (b) express it as a percentage of body weight.
17. 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.
18. What are Plimsoll Lines?
19. Define 1 Pascal.
20. State Archimedes’ Principle. Based on this principle, write its two applications.
21. Why will a sheet of paper fall slower than one that is crumpled into a ball?
22. 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?
23. Loaded test-tube placed in pure milk sinks to a certain mark (M). Now some water is mixed with the milk. Will the test tube sink more or less? Explain.
24. 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/m3.
25. Relative density of silver is 10.8. If the density of water is 103kg/m3, find density of silver.
26. Fill in the blanks :
According to the Heliocentric theory, the _____ is at centre and _______ move around it.
27. Fill in the blanks :
______ stated that every planet moves around the sun in closed elliptical orbit, with the ___ at one focus.
28. Fill in the blanks :
The force which keeps the object moving in a circular path is called _____ force. It always acts towards the _____.
29. Fill in the blanks :
The value of Universal Gravitation constant (G) is ________ Nm2kgs-2.
30. Fill in the blanks :
The value of g ________ (increases/decreases) as we go downwards from the earth's surface.
31. Fill in the blanks :
Weight of an object is the product of ______ and ________.
32. Fill in the blanks :
At the centre of the earth, the acceleration due to gravity is _______.
33. What are the Kepler Laws that govern the motion of the planets?
34. State the universal law of gravitation.
35. An object moves in a circular motion due to centripetal force, acting towards the center. The moon also rotates around the earth? Does centripetal force acts on it? Why does the moon not fall on the earth?
Q:If the moon attracts the earth, why does the earth not move towards the moon?
36. 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 whichthe moon attracts the earth? Why?
37. An object is placed at the surface of the earth and is at distance R from the center of the earth. The object weighs 180N. What will be its weight if it is at distance 3R from the center of the earth.
38. Does Law of gravitation obey Newton's third law of motion?
39. Define 'g' or acceleration due to gravity? Does it depend on the mass of the body (near the surface of the earth)experiencing 'g'?
40. (a) What is the relationship between g and G?
(b) Show mathematically whether g (acceleration due to gravity on the earth) depends on the mass of the object itself or not.
(c) Show that for a given location on the surface of the earth g is almost constant.
41. 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].
42. Is acceleration due to gravity a vector or a scalar? Write its S.I. unit.
43. Define gravity.
44. What is weightlessness?
45. Fill in the blanks :
It is the ____________ of the earth, which holds our atmosphere in place.
46. Fill in the blanks :
Universal gravitational constant G = _____________.
47. Why do sewing needles and all pins have a sharp pointed tip?
48. Fill in the blanks :
Geocentric model i.e. the Earth is the orbital centre of all celestial bodies was proposed by _____.
49. Fill in the blanks :
Heliocentric model was proposed by ______.
50. 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.
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