CBSE Class 9 Science Gravitation VBQs

Multiple Choice Questions

Question. When an object is thrown upward, the force of gravity is
(a) opposite to the direction of motion
(b) in the same direction as the direction of motion
(c) becomes zero at the highest point
(d) increases as it rises up.
Answer. A

Question. The weight of a body of mass 5 kg is
(a) 69.0 N
(b) 79.0 N
(c) 49.0 N
(d) 39.0 N
Answer. C

Question. The value of G was first determined experimentally by
(a) Newton
(b) Henry Cavendish
(c) Kepler
(d) Galileo
Answer. B

Question. Which of the following statements is/are correct?I. Mass of an object is the measure of its inertia.
II. Heavier the object smaller is the inertia.
III. The mass of an object is variable.
(a) Only I
(b) I and III
(c) II and III
(d) I and II
Answer. A

Question. If a planet existed whose mass was twice that of Earth and whose radius 3 times greater, how much will a 1 kg mass weigh on the planet?
(a) 25 N
(b) 2.17 N
(c) 1.1 N
(d) 5 N
Answer. B

Question. If g0, gh and gd be the acceleration due to gravity at earth’s surface, at height h and at a depth d respectively, then
(a) g0 > gh and g0 > gd
(b) g0 < gh and g0 < gd
(c) g0 > gh and g0 < gd
(d) g0 < gh and g0 > gd.
Answer. A

Question. The mass of a body is increased 4 fold and mass of other body is increased 16 fold. How should the distance between them be changed to keep the same gravitational force between them?
(a) 4 times
(b) 1/4 times
(c) 8 times
(d) 1/8 times
Answer. C

Question. 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 the two stones will meet.
(a) 4 s
(b) 3.6 s
(c) 2 s
(d) 8 s
Answer. A

Question. The mass of a body is measured to be 12 kg on the earth. If it is taken to the moon, its mass will be
(a) 12 kg
(b) 6 kg
(c) 2 kg
(d) 72 kg.
Answer. A

Question. A balloon of mass m is rising with an acceleration a. A fraction of its mass is detached from the balloon. Its acceleration will
(a) decrease
(b) increase
(c) remain the same
(d) none of these
Answer. B

Question. If ge is acceleration due to gravity on earth and gm is acceleration due to gravity on moon, then
(a) ge = gm
(b) ge < gm
(c) ge = 1/6 gm
(d) ge = 1/6 gm
Answer. B

Question. The unit of G/g is
(a) kg m^–1
(b) kg m^–2
(c) m2 kg^–1
(d) m kg^{–1
Answer. C}

Question. Match the List-I and II and choose correct option below.
      List-I                           List-II
(P) r³ = T² × constant      1. u = 0
(Q) v = gt                         2. Weight
(R) m × g                         3. Equation of motion
(S) v² = u² + 2gh             4. Kepler’s law
(a) P - 4, Q - 1, R - 2, S - 3
(b) P - 4, Q - 2, R - 3, S - 1
(c) P - 2, Q - 4, R - 1, S - 3
(d) P - 1, Q - 4, R - 2, S - 3
Answer. A

Question. If the mass of the body on the surface of the earth is 50 kg, its mass at the centre of the earth is
(a) zero
(b) more than 50 kg
(c) less than 50 kg
(d) equal to 50 kg
Answer. D

Question. Two identical copper spheres of radius R are in contact with each other. If the gravitational attraction between them is F, find the relation between F and R.
(a) F ∝ R⁴
(b) F ∝ R^3/2
(c) F ∝ R^–2
(d) F ∝ R^–4
Answer. A

Question. Relation between mass of body and its weight is 
(a) w = mg
(b) w = m/g 
(c) g = m – w
(d) w = m + g
Answer. A

Question. Choose the correct statement.
(a) Weight is a vector quantity.
(b) The weight of a body in interplanetary space is maximum.
(c) Weight increases when the bodies go up.
(d) 1 N = 1 kg m s^–1
Answer. A

Question. A particle is dropped from a tower 180 m high. How long does it take to reach the ground?
Take g = 10 m/s².
(a) 2 s
(b) 6 s
(c) 5 s
(d) 8 s
Answer. B

Question. The value of acceleration due to gravity is high if
(a) mass and radius both are small
(b) mass is small and radius is large
(c) mass is large and radius is small
(d) mass and radius both are large.
Answer. C

Question. A person in a spaceship moving in space, experience weightlessness as the value of
(a) mass is zero
(b) acceleration due to gravity is zero
(c) gravitational force is zero
(d) none of these
Answer. B

Question. Which of the following is correct for mass?
(a) It is a vector quantity.
(b) It is not a fundamental property of material body.
(c) It is the force with which the earth attracts a body.
(d) It is the quantity of matter contained in a body.
Answer. D

Question. What happens to the acceleration due to gravity with the increase in altitude from the surface of the earth?
(a) Increases
(b) Decreases
(c) First decreases and then increases
(d) Remains same
Answer. B

Question. An astronaut in the orbit in a spacecraft feels weightlessness
(a) due to the absence of gravity inside
(b) due to the fact that spacecraft has no energy
(c) because acceleration in the orbit is equal to acceleration of gravity outside
(d) there is no gravity outside
Answer. C

Question. An apple falls towards the earth because the earth attracts it. The apple also attracts the earth by the same force. Why do we not see the earth rising towards the apple?
(a) Acceleration of the earth is very large when compared to that of apple.
(b) Acceleration of the earth is equal to that of apple.
(c) Acceleration of the earth is neither high nor too low.
(d) Acceleration of the earth is very small when compared to that of apple.
Answer. D

Question. According to Kepler’s law the relationship between T (time period of revolution of a planet) and r (the semi-major axis of ellipse) is
(a) T² ∝ r
(b) T² ∝ r²
(c) T² ∝ r^–3
(d) T ∝ r^3/2
Answer. D

Case Based MCQs

Case I : Read the passage given below and answer the following questions.

According to universal law of gravitation, the force between two particles or bodies is directly proportional to the product of their masses and inversely proportional to the square of the distance between these particles or bodies.
Consider two bodies A and B having masses m_{1 a}nd m₂ respectively. Let the distance between these bodies be R. The force of gravitation between these bodies is given by
F ∝ m₁m₂ and  F ∝ 1/R²
F= G (m₁m₂) /R²
Where G is constant and is known as “universal gravitational constant”. 

Question. Gravitational force is a
(a) repulsive force
(b) attractive force
(c) neither (a) nor
(b) (d) both (a) and (b)
Answer. B

Question.Two particles of mass m₁ and m₂, approach each other due to their mutual gravitational attraction only. Then
(a) accelerations of both the particles are equal.
(b) acceleration of the particle of mass m₁ is proportional to m₁.
(c) acceleration of the particle of mass m₁ is proportional to m₂.
(d) acceleration of the particle of mass m₁ is inversely proportional to m₁.
Answer. C

Question.Gravitational force between two bodies is1 N. If the distance between them is made half,what will be the force?
(a) 2 N
(b) 4 N
(c) 6 N
(d) 7 N
Answer. B

Question. How does the force of gravitation between two objects change when the distance between them is reduced to half?
(a) Force of gravitation becomes 4 times
(b) Force of gravitation becomes 9 times
(c) Force of gravitation becomes 6 times
(d) Force of gravitation becomes 12 times
Answer. A

Case II : Read the passage given below and answer the following questions.

There is no atmosphere on the moon. This is because gas molecules need a certain amount of force of attraction to be retained on a heavenly body. The force of attraction of the moon is less than the required force, hence no atmosphere can exist.

Question. The value of g on moon is ........ times that of earth
(a) 1/3
(b) 1/4
(c) 1/5
(d) 1/6
Answer. D

Question. Mass of the moon is .......... that of earth
(a) more than
(b) less than
(c) equal to
(d) can’t say
Answer. B

Question. If the weight of an object is 60 kg f on earth then, its weight on moon is .......
(a) 10 kg f
(b) 20 kg f
(c) 30 kg f
(d) 40 kg f
Answer. A

Case III : Read the passage given below and answer the following questions.

All freely falling bodies fall with a uniform acceleration due to gravity. As a result, all the equations of motion for the uniformly accelerated bodies moving in a straight line are applicable to the freely falling bodies.

Question. The value of g is taken as positive when a body is
(a) dropped from a certain height
(b) moving in horizontal direction
(c) both (a) and (b)
(d) none of these
Answer. C

Question. Velocity of an object at maximum height in case it has been thrown vertically upward is
(a) maximum
(b) minimum
(c) zero
(d) 9.8 m s^–1
Answer. C

Question. During free fall, the acceleration of the object is
(a) zero
(b) non-uniform
(c) constant
(d) none of these
Answer. C

Assertion & Reasoning Based MCQs

For question, a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices.
(a) Both assertion and reason are true, and reason is correct explanation of the assertion.
(b) Both assertion and reason are true, but reason is not the correct explanation of the assertion.
(c) Assertion is true, but reason is false.
(d) Assertion is false, but reason is true.

Question. Assertion : It is the gravitational force exerted by the sun and the moon on the sea water that causes to the formation of tides in the sea.
Reason : Gravitational force of attraction is a strong force.
Answer. C

Question. Assertion : The value of acceleration due to gravity changes with the height, depth and shape of the earth.
Reason : Acceleration due to gravity is zero at the centre of the earth.
Answer. B

Question. Assertion : When distance between two bodies is doubled and also mass of each body is doubled, then the gravitational force between them remains the same.
Reason : According to Newton’s law of gravitation, force is directly proportional to the product mass of bodies and inversely proportional to square of the distance between them.
Answer. A

Question. Assertion : Any two objects in the universe attract each other by a force called gravitational force.
Reason : The force of gravitation exerted by the earth is called gravity.
Answer. B

Question. Assertion : Universal gravitational constant G is a scalar quantity.
Reason : The value of G is same through out the universe.
Answer. B

Question. Assertion : When a body is thrown up, the acceleration due to gravity at the topmost point is zero.
Reason : The acceleration due to gravity is always directed towards the centre of the earth for a freely falling body.
Answer. D

Question. Assertion : If we drop a stone and a sheet of paper from a balcony of first floor, then stone will reach the ground first.
Reason : The resistance due to air depends on velocity only. 
Answer. C

Question. Assertion : Kepler’s second law of planetary motion is also known as Kepler’s law of areas.
Reason : The line joining the planet and the sun sweeps equal areas in equal intervals of time.
Answer. A

Question. Assertion : A sheet of paper falls slower, than one that is crumpled in to a ball?
Reason : Sheet of paper has lesser weight than that is crumpled into a ball.
Answer. C

Very Short Answer Type Questions

Question. At what place on the earth’s surface is the weight of a body maximum?
Answer. At the poles, weight of the body is maximum.

Question. State the Kepler’s third law.
Answer. The square of the time period of revolution of a planet is proportional to the cube of the semi-major axis of the ellipse traced out by the planet.

Question. Why is G called the universal gravitational constant?
Answer. The constant G is universal because it is independent of the nature and size of bodies, the space where they are kept and at the time at which the force is considered.

Question. What is the ratio of the force of attraction between two bodies kept in air and the same distance apart in water?
Answer. 1 : 1, because the gravitational force does not depend on the nature of the medium.

Question. What is the centripetal force?
Answer. The force required for a body to move in a circular path is called centripetal force.

Question. The weight of a body is 50 N. What is its mass? (g = 9.8 m s^–2)
Answer. Here, W = 50 N
g = 9.8 ms^–2
we have, mass =W/g =  50N/9.8 ms^–2
Mass = 5.10 kg

Question. Define universal gravitational constant.
Answer. The universal gravitational constant is the force of attraction between two point masses of 1 kg each kept at a distance of 1 m.

Question. Which is more fundamental-mass or weight of a body?
Answer. Mass is more fundamental than weight because the mass of a body remains constant while its weight changes from place to place due to change in the value of g.

Question. Newton’s law of gravitation is also called inverse square law. Why is it so called?
Answer. According to Newton’s law of gravitation, the magnitude of the gravitational force between two objects is inversely proportional to the square of the distance between them, i.e.,
F ∝ 1/r 2 . That is why this law is also called inverse square law.

Question. Suppose gravity of Sun suddenly becomes zero, then in which direction will the Earth begin to move if no other celestial body affects it?
Answer.  The Earth will move in the direction of the tangent to the Sun orbit.

Short Answer Type Questions

Question.When does an object show weightlessness?
Answer. Weightlessness is a state when weight of an object is zero. It occurs when a body is in a state of free fall under the effect of gravity alone.

Question. What is the acceleration of free fall?
Answer. When a body is released from a height, it begins to fall freely due to earth’s gravitational force acting on it. Due to this force, the body experiences an acceleration towards centre of earth. This acceleration is the acceleration of free fall and is called the acceleration due to gravity.

Question. What is the source of centripetal force that a planet requires to revolve around the sun? On what factors does that force depend?
Answer. Gravitational force. This force depends on the product of the masses of the planet and sun and the distance between them.