# Engineering Physics Questions and Answers – Mass and Density of the Earth

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This set of Engineering Physics Multiple Choice Questions & Answers (MCQs) focuses on “Mass and Density of the Earth”.

1. If the density of the planet is doubled without any change in its radius, how does g change on the planet?
a) It remains the same
b) It is tripled
c) It reduces
d) It is doubled

Explanation: If the density of the planet is doubled without any change in its radius, g also gets doubled, because g is proportional to the density of the planet.

2. A body can be shielded from gravitational effects.
a) True
b) False

Explanation: No, it is not possible to shield a body from gravitational effects because gravitational interaction does not depend upon the nature of the intervening medium.

3. Gravity acts on all bodies in proportion to their masses; therefore heavy body falls faster than light body.
a) True
b) False

Explanation: If F id the gravitational force on a body of mass m, then
F=G Mm/R2 = mg
Or g=GM/R2
Clearly, F is proportional to mass but g does not depend on m. Therefore all bodies fall with the same rapidness if there is no air resistance.
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4. The mass of the moon is nearly 10% of the mass of the earth. What will be the gravitational force of the earth on the moon, in comparison to the gravitational force of the moon on the earth?
a) Both of the force will be equal
b) Gravitational force of the earth on the moon is much lesser
c) Gravitational force of the moon on the earth is much lesser
d) There is no effect

Explanation: If the mass of the moon is 10% of the mass of the earth, then the gravitational force of the earth on the moon will be equal in comparison with the gravitational force of the moon on earth. This is because the gravitational force between the two bodies id a mutual force.

5. A man waves his arm while walking. This is ____________
a) To keep constant velocity
b) To ease the tension
c) To increase the velocity
d) To balance the effect of earth’s gravity

Explanation: The waving of the arm helps in keeping the centre of gravity at a suitable position. This helps the man to walk comfortably.

6. Kepler’s second law is based on ___________
a) Newton’s first law
b) Newton’s second law
c) Special theory of relativity
d) Conservation of angular momentum

Explanation: Kepler’s second law states that the radius vector drawn from the sun to a planet, sweeps out equal areas in equal intervals of time. It is based on the law of conservation of angular momentum.

7. Statement 1- An astronaut experiences weightlessness in a space satellite.
Statement 2- When a body falls freely, it does not experience gravity.
a) Statement 1 and statement 2 are correct and statement 2 is the correct explanation of statement 1
b) Statement 1 and statement 2 are correct but statement 2 is not the correct explanation of statement 1
c) Statement 1 is true but statement 2 is false
d) Both statement 1 and 2 are false

Explanation: Both statements are true but statement 2 is not the correct explanation of statement 1. The astronaut feels weightlessness because both the astronaut and the satellite are in a state of free fall towards the earth.

8. Two spheres of masses m and M are in air and the gravitational force between them is F. The space around the masses is now filled with liquid of specific gravity 3. The gravitational force will now be ___________
a) 3F
b) F
c) F/3
d) F/9

Explanation: The gravitational force between the two bodies is independent of the nature of the medium between them.

9. For a satellite escape velocity from the earth is 11.2 km/s. If a body is to be projected in a direction making an angle 45° to the vertical, then what is the escape velocity?
a) 11.2×2km/s
b) 11.2km/s
c) 11.2×√2km/s
d) 11.2/√2km/s

Explanation: Escape velocity does not depend on the angle of the projection of the body from the earth’s surface. Therefore v = 11.2 km/s.

10. If earth loses its gravity, then for a body ___________
a) A weight becomes zero, but not the mass
b) Mass becomes zero but not weight
c) Neither mass nor weight becomes zero
d) Both mass and weight are zero

Explanation: Weight = mg. As g becomes zero. Mass is the quantity of matter which is dependent on g.

11. A ball is dropped from a spacecraft revolving around the earth at a height of 120km. What will happen to the ball?
a) It will go very far in space
b) It will move with the same speed tangentially to the spacecraft
c) It will fall down to the earth gradually
d) It will continue to move with the same speed along the original orbit of spacecraft

Explanation: In the absence of any external torque, the ball will continue to move at the same speed along the original orbit of space craft.

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