Gravitation Class 9 Worksheet Science Chapter 9

Multiple Choice Questions

Q1: If the area of an object is less than the pressure acting on that object will be
(a) Less
(b) More
(c) Independent of area
(d) None of the above
Ans: (b)

Q2: Even though stone also attracts earth towards itself, earth does not move
(a) Because of greater mass of earth
(b) Because of lesser mass of stone
(c) Force exerted by stone is less
(d) Force exerted earth is large
Ans: (a)

Q3: Which of the statements is correct?
(a) Mass is constant and weight is variable
(b) Mass is variable and weight is constant.
(c) Both Mass and weight are variable
(d) Both Mass and weight are constant.
Ans: (a)

Q4: Weight of the object is:
(a) More at the equator and less at poles
(b) More at poles and less at equator
(c) Same at poles and equator
(d) Depend on Mass of the object
Ans: (b)

Q5: An object is put one by one in three liquids having different densities. The object floats with 1/9, 2/11 and 3/7 parts of their volumes outside the liquid surface in liquids of densities d₁, d₂ and d₃respectively. Which of the following statement is correct?
(a) d₁ > d₂ > d₃
(b) d₁ > d₂ < d₃
(c) d₁ < d₂ > d₃
(d) d₁ < d₂ < d₃ 
Ans: (d) 

Q6: In the relation F = GM mld², the quantity G
(a) depends on the value ofg at the place of observation
(b) is used only when the Earth is one of the two masses
(c) is greatest at the surface of the Earth
(d) is universal constant of nature
Ans: (d)

Q7: Law of gravitation gives the gravitational force between
(a) the Earth and a point mass only
(b) the Earth and Sun only
(c) any two bodies having some mass
(d) two charged bodies only
Ans: (c) 

Q8: The value of quantity G in the law of gravitation
(a) depends on mass of Earth only
(b) depends on radius of Earth only
(c) depends on both mass and radius of Earth
(d) is independent of mass and radius of the Earth
Ans: (d) 

Q9: Two particles are placed at some distance. If the mass of each of the two particles is doubled, keeping the distance between them unchanged, the value of gravitational force between them will be
(a) 1/4 times
(b) 4 times
(c) 1/2 times
(d) unchanged
Ans: (b)

Q10: The atmosphere is held to the Earth by
(a) gravity
(b) wind
(c) clouds
(d) Earth’s magnetic field 
Ans: (a)

Fill in the blank

(i) The value of g on the earth is about Six times of that on the moon.
(ii) In fluids (liquids and gases), pressure acts in All directions, and pressure increases as the depth increases.
(iii) If the area of a snow shoe is five times Bigger than the area of an ordinary shoe, then the pressure of a snow shoe on the snow is five times smaller.
(iv) Force acting on a unit area is called Pressure.
(v) The weight of an object on the earth is about Six times of its weight on the moon.

Crossword

Across

3. Quantity of matter contained in a body
4. The property due to which a body immersed in fluid experiences upward force.
5. Acceleration due to gravity of moon is how much time that of Earth
7. Whenever objects fall towards the Earth under gravitational force alone, we say that objects are in
8. The force with which a body is attracted towards the Earth
10. Force of gravitation due to Earth is called
11. Nature of gravitational force is always

Down

1. Force between two bodies due to their masses
2. Thrust on unit area
6. Mass per unit volume
9. SI unit of pressure

Ans:

Across:
3. Mass
4. Buoyancy
5. One sixth
7. Free fall
8. Weight
10. Gravity
11. Attractive

Down:
1. Gravitational force
2. Pressure
6. Density
9. Pascal

Very Short Answer Questions

Q1: A man of mass 60 Kg is standing on the floor holding a stone weighing 40 N. What is the force with which the floor is pushing him up?
Ans: The gravitational pull on the man = Mg
= 60 x 10 = 600 N
The weight he is carrying = 40 N
The total downward force on the floor = 40 N + 600 N
= 640 N
The Gravitational force and upward force of the floor is an action – reaction pair.
The force with which the floor pushes the man = 640 N.

Q2: State Archimedes Principle?
Ans: According to Archimedes Principle when a body is partially or completely immersed in a fluid, experiences an up thrust which is equal to the weight of fluid displaced.

Q3: Why does a block of plastic released under water come up to the surface of water?
Ans: Since of plastic has density very less as compared to water i.e. weight of plastic is less than the buoyant force experienced by it therefore a block of plastic released under water come up to the surface of water/floats.

Q4: Why will a sheet of paper fall slower than one that is crumpled into a ball?
Ans: A greater surface area offers greater resistance and buoyancy same is true in the case of a sheet of paper that has larger surface area as compared to paper crumpled into a ball. So sheet of paper falls slower.

Q5: Why is it difficult to hold a schoolbag having a strap made of a thin and strong string?
Ans: It is difficult to hold a schoolbag having a strap made of a thin and strong string because a bag of that kind will make its weight fall over a small area of the shoulder and produce a greater pressure that makes holding the bag difficult and painful.

Q6: What makes a body to float or sink in a liquid?
Ans:

• When an object is immersed in a liquid, it exerts a weight in the downward direction and the liquid exerts a force called up thrust in the upward direction on the object.
• If the object sinks in the liquid, then the weight of the body is greater than the up thrust acting on the object by the liquid.
• If the object floats in the liquid, then the weight of the body is less than the up thrust acting on the object by the liquid.

Q7: What is the importance of universal law of gravitation?
The universal law of gravitation is important due to the following:
Ans:

• This law explains well the force that binds us to earth.
• This law describes the motion of planets around the sun.
• This law justifies the tide formation on earth due to moon and sun.
• This law gives reason for movement of moon around earth.

Q8: 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?
Ans:

(i) The force between two objects will be doubled.
(ii) The force between two objects will become 1/4th and 1/9th of the present force.
(iii) The force between two objects will become four times the present force.

Q9: State the universal law of gravitation.
According to Newton’s universal law of gravitation:
Ans: Every mass in this universe attracts every other mass with a force which is directly proportional to the product of two masses and inversely proportional to the square of the distance between them.

Q10: What do you mean by buoyancy?
Ans: It is the upward force experienced by an object when it is immersed into a fluid.