HOTS Questions: Gravitation | Science Class 9 PDF Download

Q1: The S.I. unit of G is 
(a) Nkg²/m²
(b) Nm²/kg²
(c) N²m/kg
(d) Nm/kg²
Ans: (b)

The universal gravitational constant is represented by ‘G’. S.I. unit of universal gravitational constant is Nm²/Kg². As G = Fxr²/Mm.

Q2: The mass of the body on the moon is 40kg. What is the weight on the Earth? 
(a) 240kg      
(b) 392N      
(c) 240N      
(d) 400kg
Ans: (b)

Given The mass of the body on moon is 40 kg , what is the weight on the earth ?

Now we have mass of body on moon m = 40 kg.

We know that weight on earth is given by mass x gravitational force

 So w = m x g

       w = 40 x 9.8 m/s²

      w = 392 N

So weight on the earth is 392 N

Q3: A body is thrown upwards. What is the direction of ‘g’ when the body is falling down 
(a) upwards
(b) downwards
(c) both a and b
(d) can’t be said
Ans:  (b)

When a body is thrown upwards, the direction of ‘g ‘ is negative that slows down the speed of body. When the body is falling downward, the direction of ‘g’ is downward.

Q4: Two objects of different masses are dropped freely from a height near the surface of earth they have
 A. Different velocities at any instant
 B. Same velocities at any instant 
 C. Different accelerations
 D. Same acceleration  
(a) B and C are correct
(b) B and D are correct
(c) A, B and C are correct
(d) All of these
Ans: (b)

​The correct option is B.
Objects of different masses falling freely near the surface of the earth would have the same velocities at any instant because they will have the same acceleration due to gravity.

Q5: Inverse square law means F α? 
(a) 1/r
(b) 1/r²
(c) 1/r⁴
(d) 1/r³
Ans:  (b)

The force acting on two bodies is inversely proportional to square of the distance between them. Therefore, Fα 1/r².

Q6: Which of the two statements is true? 
Statement A: Polar radius is 6357km and equatorial radius is 6378 km.
Statement B: At a given place, the weight of an object is equal to the mass of the object.
(a) Statement A
(b) Statement B
(c) Both A and B
(d) Neither A nor B
Ans:  (a)

Polar radius is 6357 km and equatorial radius is 6378 km. The shape of earth is not perfectly spherical. Poles are slightly closer to centre of earth. Weight of body at particular place is product of mass and acceleration due to gravity. So, weight and mass of body at particular position never be equal.

Q7: A man throws a ball with a velocity of 20m/s. After what time will the ball come back to his hands? (Take g = 10m/s²) 
(a) 8 s
(b) 2 s
(c) 3 s
(d) 4 s
Ans: (d)

Initial velocity ,u= 20 m/s. final velocity = o , g = 10ms⁻² .
 v = u + gt,
 0 = 20+(−10)×t
 t = 20/10 = 2s.
 Time taken to fall in downward direction = 2s. Hence total time taken = 2s +2s = 4s.

Q8: A stone falling towards Earth.
Statement A. Is attracted by earth
Statement  B. Attracts the earth 
Statement  C. Both stone and earth attract each other 
Statement  D. No one attracts each other 
(a) A and B are correct
(b) B and C are correct
(c) A, B and C are correct
(d) All of these
Ans: (c)

When a stone falls toward the Earth:

• Statement A: The stone is attracted by Earth — Correct

• Statement B: The stone also attracts the Earth — Correct, although the effect is too small to notice because the Earth's mass is so large.

• Statement C: So, both the Earth and stone attract each other — Correct

• Statement D: Incorrect, because both objects do exert a gravitational force.

Q9: What is 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? 
(a) 6:1
(b) 1:1
(c) 1:6
(d) None of these
Ans:  (b)

The force of gravitation is equal to the product of masses divided by the square of the distance between them. So, the force of gravitation between two bodies will be the same irrespective of their place. 

So, the ratio will be 1:1.

Q10: The Gravitation force is a 
(a) short-range force
(b) non-central force
(c) weakest force
(d) strongest force
Ans: (c)

Gravitational force is a weak force. This force exists between each and every object but cannot be felt until the mass of the bodies is extremely high, like planets.

Q11: Which of the following is true of two objects of different masses falling freely near the surface of the moon? 
(a) They both have different accelerations.
(b) They experience forces of the same magnitude
(c) They have the same velocities at any instant
(d) They change their inertia
Ans: (c)

They have the same velocities at any instant.
Two different masses falling freely near the moon’s surface have the same velocities at any instant.

Q12: What will be the pressure when a force of 200N it’s exerted on an area of 5m² 
(a) 40 Pa
(b) 45 Pa
(c) 30 Pa
(d) 35 Pa
Ans: (a)

Pressure = Force/ area. Here, Force = 200N  Area=5m². So, pressure = 200N / 5m ²= 40 Pa.

Q13: The value of G depends on 
(a) Distance between the bodies
(b) Some other masses kept nearby
(c) masses of the bodies
(d) None of these
Ans: (d)

​The value of the universal gravitational constant (G) is 6.67×10⁻¹¹Nm²/Kg²which is constant and independent of mass, distance between the bodies and other factors.

Q14:  Which of the two statements is true? 
Statement A: The Earth attract the moon with a force greater than the force with which the moon attracts the Earth. 
Statement B: The mass and weight of a body become O at the centre of the Earth.
(a) Statement A
(b) Statement B
(c) Both statements A and B
(d) Neither statement A nor B.
Ans: (d)

Earth and Moon attract each other with equal gravitational force. The mass of a body never becomes 0. Hence, both statements are incorrect.

Q15: What is the weight of a body whose mass is 100 kg on the surface of the Earth? 
(a) 500N
(b) 100N
(c) 980N
(d) 490N
Ans:  (c)

Mass of the body (m) = 100 kg, acceleration due to gravity (g) =9.8 m/s. Weight (w) = m×g=100×9.8= 980N.

Q16: In which of the following pressures is increased 
 A. The strap of the bag is made wider
 B. Knife with a sharp edge 
 C. Shoes with a flat sole
 D. Nail with a finely pointed tip  
(a) B and C are correct
(b) A, B and C are correct
(c) B and D are correct
(d) All of these
Ans: (c)

A. The strap of the bag is made wider
→ Area increases, so pressure decreases — Not correct

B. Knife with a sharp edge
→ Sharp edge = small area → high pressure — Correct

C. Shoes with a flat sole
→ Flat sole = larger area → low pressure — Not correct

D. Nail with a finely pointed tip
→ Pointed tip = small area → high pressure — Correct

Q17: Two masses m and M are kept at a distance r. The ratio of the force exerted on m due to M and that of M due to m is equal to 
(a) 1:1
(b) M/m
(c) Mr/M
(d) None of these

Ans: a

Gravitational force between two bodies F = G Mm/r². 

• The force on m due to M = $\mathrm{<br>}F$F

• The force on M due to m = $\mathrm{<br>}F$F

Q18: Force of gravitation
 A. Directly proportional to the product of masses of two objects 
 B. Inversely proportional to the product of masses of two objects 
 C. Directly proportional to the square of distance between two objects
 D. Inversely proportional to the square of distance between two objects  
(a) A and  D are correct
(b) A, B and C are correct
(c) B and C are correct
(d) All of these
Ans: (a)

According to Newton’s Universal Law of Gravitation:

F = G m₁m₂/r²

Where:

• F is the gravitational force

• $m\_1$m1 and m2 are the masses of the two objects

• $\mathrm{<br>}r$r is the distance between the centers of the two objects

• $\mathrm{<span>G\; is\; the\; universal\; gravitational\; constant</span>}$

• A. Directly proportional to the product of masses of two objects
  → Correct, as F∝m₁⋅m₂

• B. Inversely proportional to the product of masses
  → Incorrect, it’s directly proportional, not inversely.

• C. Directly proportional to the square of distance
  → Incorrect, it's inversely proportional to the square of distance.

• D. Inversely proportional to the square of distance
  → Correct, as $F\; \backslash propto\; \backslash frac\{1\}\{r^2\}$F∝ 1/r²

Q19: The weight of an object is greatest at some region of the earth. What will be the colour of bears found in that region? 
(a) black
(b) white
(c) blue
(d) brown
Ans: (b)

The weight of an object is greatest at the poles of the Earth because:

• The Earth is not a perfect sphere; it is slightly flattened at the poles and bulged at the equator.

• As a result, the distance from the center of the Earth is shortest at the poles, which increases gravitational force.

• Gravitational force (and thus weight) is greater at the poles compared to the equator.

The polar regions, especially the Arctic, are home to polar bears, which are white in color to blend with the snow and ice.

Q20: What is buoyant force- 
(a) An upward force on an object immersed in a liquid
(b) Partially downward force
(c) A down ward force on an object immersed in a liquid
(d) None of the above.
Ans: (a)

When an object is immersed in a liquid (fully or partially), the liquid exerts an upward force on the object. This force is called the buoyant force or upthrust.

• This upward force is what makes objects feel lighter in water.

• The buoyant force acts in the opposite direction of gravity, helping some objects to float.