Railway Science (Physics-Gravitation)

Total Questions: 59

41. What will be the ratio of gravity at a depth h from the Earth's surface and at a height h from the Earth's surface, where the radius of the Earth is h < <: [RRB Group D 2/11/2018 (Morning)]

Correct Answer: (d) will increase linearly with h
Solution:

The earth can be imagined to be a sphere made of a large number of concentric spherical shells with the smallest one at the center and the largest one at its surface. The gravitational force between the spherical balls is the same as if their masses are concentrated at their centers.

42. In the absence of gravitational force of attraction, the thrust on a rocket is ________: [RRB Group D 16/11/2018 (Afternoon)]

Correct Answer: (d) stable
Solution:

The gravitational force of attraction is described by Newton's law of universal gravitation. Newton's law of universal gravitation:
F = 𝐺𝑚₁𝑚₂/r².

43. Which of the following statements is false? [RRB Group D 06/12/2018 (Evening)]

Correct Answer: (b) The value of 'g' depends on the mass of the falling object.
Solution:

The value of g does not depend upon shape, size or mass of the body. The value of acceleration due to gravity of the earth, g = 9.8 ms² . The earth is not a perfect sphere. As the radius of the earth increases from the poles to the equator, the value of g becomes greater at the poles than at the equator.

44. At which of the following places the acceleration due to gravity is zero? [RRB Group D 10/12/2018 (Morning)]

Correct Answer: (c) at the center of the earth
Solution:

The value of g is least at the equator and maximum at the poles. It means the value of acceleration due to gravity increases as we go from the equator to the poles. Thus, the gravitational force at the center of any body will be 0. The average gravitational pull of the Earth is 9.8 meters per second square (m/s² ). Gravitational Force : The attracting force that exists between any two bodies in the universe.

45. The value of universal gravitation constant (G) was determined by: [RRB ALP Tier - I (09/08/2018) Evening]

Correct Answer: (b) Henry Cavendish
Solution:

John Dalton - (Modern atomic theory, study color blindness). Isaac Newton - Universal law of gravity, Newton’s laws of motion, {(In 1686 in his book ‘Principia Mathematica Philosophiae Naturalis) - Newton's Law of Inertia, Newton's Law of Acceleration, Newton's Law of Action and Reaction)}. Antoine L Lavoisier (law of conservation of mass).

46. Fill in the blank with the most appropriate option. The Universal Constant of Gravitation is ______. [RRB ALP Tier - I (17/08/2018) Afternoon]

Correct Answer: (c) 6.67 × 10⁻¹¹ Nm²/kg²
Solution:

Accordingly to Newton's Law of Universal Gravitation, The gravitational constant is the proportionality constant which is denoted by G. Newton's law of universal gravitation: The attractive force between two objects (F) is equal to G times the product of their masses (M₁ , M₂) divided by the square of the distance between them (r²). F = G 𝑀₁ × 𝑀₂ /r² .

47. The acceleration due to gravity at the surface of the earth (mass M and radius R) is proportional to ______. [RRB ALP Tier - I (17/08/2018) Evening]

Correct Answer: (b) 𝑀/𝑅²
Solution:

The force acting on an object due to gravity is f = mg. Where f is the force acting on the object, g is the acceleration due to gravity, and m is the mass of the object. Universal gravitation, f = 𝐺𝑚𝑀/(𝑟 + ℎ)², f = force between two bodies, G = universal gravitational constant (6.67 × 10⁻¹¹ Nm²/kg²), m = mass of an object, M = mass of earth, r = radius of the Earth, h = height the object is from the earth's surface. Since the height (h) is negligible relative to the radius of the earth, the equation as f = 𝐺𝑚𝑀/𝑟²
Balance the equation - mg = 𝐺𝑚𝑀/𝑟², g = 𝐺𝑀/𝑟². (where G is constant).,

48. Which of the following statements is/are correct? [RRB ALP Tier - I (30/08/2018) Afternoon]

A. The ratio of the force of gravitation between two masses, 𝑚₁ and 𝑚₂  , kept at a distance R on the earth and on the moon is 1:
B. 𝑁𝑚²/𝑘𝑔² is the SI unit of G (Universal Gravitational Constant).
C. The value of G depends on the distance between the bodies.
D. The value of G depends on the masses of the bodies.

Correct Answer: (a) Only B
Solution:The ratio of the force of gravitation between two masses, m₁ and m₂ , kept at a distance R on the earth and on the moon, the ratio of masses cannot be the same in ratio as gravity on both earth and moon is 1:6. The law of gravitation states that the force acting between two masses depends directly on the product of their masses and inversely proportional to the square of their distance between them.

49. Calculate the work done by the force of gravity when a satellite moves in an orbit of radius 40,000 km around the earth. [RRB ALP Tier - I (31/08/2018) Morning]

Correct Answer: (d) 0 J
Solution:

When a satellite moves around the Earth in a circular path, then the force of gravity acts on it directed towards the centre. The motion of the satellite is in the horizontal plane. Therefore, the force of gravity of Earth on the satellite and the direction of motion of the satellite are perpendicular to each other. Therefore, net work done = F. s cos 90°= 0. That is, the work done by the force of gravity on a satellite moving around the Earth is zero. The work done is maximum at θ = 0º and minimum at θ = 90º.

50. Which of the following statements is/are INCORRECT? [RRB ALP Tier - I (31/08/2018) Evening]

A. The value of G on the moon is equal to that on the earth.
B. 26.68 × 10⁻¹¹ N is the force of gravitation between two point masses of 2 kg and 2 kg kept 1 m apart
C. Newton's law of gravitation is valid in the laboratory only.
D. Force is inversely proportional to the square of the distance between two bodies.

Correct Answer: (a) Only C
Solution: