Gravity MCQ Quiz - Objective Question with Answer for Gravity - Download Free PDF

• Centre of gravity is an imaginary point in a body of matter where the entire weight of an object acts.
• This is sometimes useful in designing static structures (e.g., buildings and bridges) or tp predict the behaviour of a moving body when it is acted on by gravity.

The correct answer is More than the true weight.

Key Points

• When a lift is accelerating upwards, the apparent weight of a body increases due to the additional force exerted by the acceleration of the lift.
• The apparent weight is the force experienced by the body due to the normal force exerted by the floor of the lift.
• The apparent weight is the sum of the true weight and the force due to the lift’s acceleration: Apparent Weight = True Weight + (Mass × Acceleration).
• As a result, when the lift accelerates upwards, the body feels heavier, and the apparent weight becomes greater than the true weight.

Additional Information

• True Weight is the gravitational force acting on the body, calculated as W = mg, where m is the mass of the body and g is the acceleration due to gravity.
• Apparent Weight is the normal force exerted by the floor of the lift, and it can vary depending on the lift's motion (upward or downward acceleration).
• When the lift is at rest or moving with constant velocity, the apparent weight is equal to the true weight.
• When the lift accelerates downward, the apparent weight decreases as the normal force exerted by the floor becomes less than the true weight.
• This concept is derived from Newton’s Second Law of Motion, which states that the force is the product of mass and acceleration.
• The change in apparent weight is a common demonstration of the effects of acceleration on a body in a non-inertial frame of reference, like a lift.

The correct answer is option 3.

Key Points

• The weight of an object is a measure of the gravitational force acting on it.
• On the moon, gravity is about 1/6th as strong as on Earth.
• Therefore, an object will weigh less on the moon compared to its weight on Earth.
• The correct statement is that the weight of a given object is 6 times higher on the Earth as compared to its weight on the moon.
• This difference in weight is due to the variation in gravitational acceleration between the Earth and the moon.

Additional Information

• Gravitational Force
  • This force is responsible for the weight of an object on a planetary body.
  • It varies depending on the mass and radius of the planetary body.
• Mass vs. Weight
  • Mass is a measure of the amount of matter in an object and remains constant regardless of location.
  • Weight depends on the gravitational force and can change with location.
• Gravitational Acceleration
  • On Earth, it is approximately 9.81 m/s².
  • On the moon, it is about 1.63 m/s², which is approximately 1/6th of Earth's gravitational acceleration.

The correct answer is less than that on the earth. 

Explanation:

• The value of the acceleration due to gravity (g) on the surface of the moon is less than that on the Earth. 
• This value is determined by the mass of the Earth and the distance from its center to the surface.
• On Earth, the average value of g is approximately 9.8 m/s², while on the moon, it is only about 1.625 m/s². 
• This significant difference in the value of the acceleration due to gravity is primarily due to the moon's smaller mass and size compared to Earth.

Thus, the value of g on the surface of the moon is less than that on the earth.

CONCEPT:

Gravitational Force

• The gravitational force between two objects is given by Newton's law of gravitation:

  F = G * (m1 * m2) / r^2

• Where:
  • F is the gravitational force
  • G is the gravitational constant
  • m1 and m2 are the masses of the two objects
  • r is the distance between the centers of the two objects

EXPLANATION:

• Given:
  • The ratio of the masses of the two planets (m1/m2) = 1/7
  • The ratio of their diameters (d1/d2) = 2/1
• The distance between the centers of the two planets will be proportional to their diameters. Hence, the ratio of the distances (r1/r2) = 2/1.
• Using the formula for gravitational force:
  • F1 = G * (m1 * m2) / (r1)^2
  • F2 = G * (m1 * m2) / (r2)^2
• Since m1/m2 = 1/7 and r1/r2 = 2/1:
  • F1/F2 = (G * (m1 * m2) / (r1)^2) / (G * (m1 * m2) / (r2)^2)
  • = (r2)^2 / (r1)^2
  • = (1/2)^2
  • = 1/4
• Hence, the ratio of the forces which they exert on each other (F1/F2) is 1 : 1.

Therefore, the ratio of the forces which they exert on each other is 1 : 1.

The correct answer is At the centre of the Earth.

• The centre of the Earth is such that if we are at that place, the mass around us can be considered to be condensed at the surface of the Earth itself, i.e considering the Earth as a spherical shell.
• Inside a spherical shell, there is no change in potential as one moves inside, and since only a change in potential implies a force there is no force.
• Hence the acceleration due to gravity is zero at the centre of the Earth.

• Let the mass of the earth be M.
• Mass of the other object on earth is m.
• We know the value of Gravitational Constant (G) = 6.67259 × 10^-11 Nm²/kg².
• We know the formula for the force between two objects (F) = G m¹ m²/r².
• Now the radius of the earth (r) = 6.3781 × 10⁶ m.
• We know that F = mg
• Now by substituting the values, we get mg = G M m/r².

M = g r²/G

M = (9.81) (6.3781 × 10⁶)²/6.67259 × 10^-11

M = 6 × 10²⁴ kg.

The correct answer is 127.14 N.

Concept:

• Mass: It is defined as the amount of matter it contains.
  • It is measured in kg /g /milligram etc.
  • It is a scalar quantity and has only magnitude.
  • It is not changing due to the position.
  • It is measured with Physical balance, beam balance, etc.

• Weight: It is defined as a measure of the pull of gravity on an object.
  • It is a kind of force and measured in Newton.
  • It is measured as weight (W) = mass (M) × gravity (acceleration due to gravity).
  • It is a vector quantity as it has magnitude as well as direction.
  • It could change according to position, like on the moon or any other planet.
  • It is measured with a spring balance.

Calculation:

Given, M = 78 Kg and g = 1.63 m/s²

W = M × g ⇒ 78 × 1.63 = 127.14 Newton

Hence the weight on the moon of the man is 127.14 N

Mistake Points

Do not go blindly with 1/6 of weight terms on the moon.

Here already given the acceleration on moon 1.63 m/s² 

• Weight is a measure of the force of gravity acting on an object.

Concept:

Explanation:

From the above explanation, we can see that

The gravitational pull by the earth is equal to the weight of the object.
The weight of any object on the planet is given by:

Weight (W) = m g = Force due to gravity

Where

m is mass

g is acceleration due acceleration of the planet.

The correct answer is 40m.

Key PointsInitial velocity(u) = 30m/s

Acceleration due to gravity(g)= 10 m/s2

Time (t) = 4 s

Using the equation,

S = Ut + 1/2 × a× t²

S = 30 × 4 + 1/2 ×  (-10) × 4× 4 

= 120 - 80

= 40 m

The correct answer is 60 kg.

Key Points

• The mass of man on the surface of the moon will remain the same as on earth.
• Mass doesn’t change according to location.
• The mass of a body is the same on Earth and Moon and is equal to 60kg.
• Mass is the measure of the amount of matter in a body.
• The SI unit of mass is kilogram (kg).
• Mass is a scalar quantity and It has magnitude.
• The mass of a body is not dependent on time.
• Mass is not dependent on gravity.
• Mass can never be zero.

Mistake Points

• Weight is defined as a measure of the gravitational force on that body at that place.
• Weight = Mass x Surface Gravity.
  • Surface Gravity on Moon = \({1\over6}{Surface \ Gravity\ on\ Earth}\)
  • Surface Gravity on Earth= 9.8 m/s².
• \(Weight \ on \ moon = 60 \times {{1\over6}\times{9.8}}\)
• Weight on moon= 98 N.

The correct answer is Galileo Galilei.

Key Points

• Galileo Galilei was the first to conclude that in vacuum all objects fall with the same acceleration g and reach the ground at the same time.
• The acceleration of the object equals the gravitational acceleration.
  • The mass, size, and shape of the object are not a factor in describing the motion of the object.
  • So all objects, regardless of size or shape, or weight, free fall with the same acceleration.
  • In a vacuum, a feather falls at the same rate as a ball.
  • The remarkable observation that all free-falling objects fall with the same acceleration was first proposed by Galileo Galilei.

Important Points

• Galileo conducted experiments using a ball on an inclined plane to determine the relationship between the time and distance traveled.
  • He found that the distance depended on the square of the time and that the velocity increased as the ball moved down the incline.
  • The relationship was the same regardless of the mass of the ball used in the experiment.
  • The experiment was successful because he was using a ball for the falling object and the friction between the ball and the plane was much smaller than the gravitational force.

• The force of gravitation between two bodies in the universe does not depend on the sum of their masses.
• It depends on distance, gravitational constant, and the product of their masses.
• The strength of the gravitational force depends on distance and mass.
• Gravitational force is that which attracts any 2 objects with mass.

The correct answer is Option (4) i.e.​ (6.67 × 10-8) c.g.s unit.

Mistake Points

•  The value of universal gravitational constant G in CGS system (Centimeter, Gram, Second) is 6.67 × 10-8 dyne cm2gm-2.
• The value of the gravitational constant in MKS system (Meter, Kg, Second) is G = 6.67×10−11 m³kg−1s−2.

Explanation:

• Universal Gravitational Constant (G): The universal constant relating force to mass and distance in Newton's law of gravitation (G), constant of gravitation, gravitational constant type of constant, a number representing a quantity assumed to have a fixed value in a specified mathematical context.
• Value of G = 6.67 × 10-8  c.g.s. Unit.
• Mathematical form: 
  • F = Gravitational Force.
  • M1 & M2 = Mass of 2 different objects which attract each other.
  • G = Universal gravitational constant.

\(F = G\frac{{{M_1}\;{M_2}}}{{{R^2}}}\)

• From this above equation, we can say that the gravitational force is the direct proportionate with the mass of two significant objects but the inverse proportional with the square of the distance(R) between those two objects.

Gravitational force: 

• The gravitational force (F) is a force that attracts any two objects with a mass within a universe.

• Every object, including you, is pulling on every other object in the entire universe. This is called Newton's Universal Law of Gravitation.

• Example of Gravitational force (F):
  1) The force that holds the gases in the sun.
  2) The force that causes a ball you throw in the air to come down again.

The correct answer is Mass.

• The acceleration (Acceleration due to gravity) experienced by an object during a free fall is independent of its mass.
• This acceleration is called acceleration due to the earth’s gravitational force. It is denoted by g.
• The unit of g is ms^-2.

As we know that

F = G.M.m/r² = mg       (F= ma , Second law of Newton)

Where F is the gravitational force, G is universal gravitation, M mass of earth, and m is the mass of the object(body). 
canceling out the Mass of the object (m)
we get;

g = G.M/r² 

So we can see that acceleration due to gravity(g) is independent of the mass of the object(body).