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Gravitation & Pressure — Homi Bhabha Exam Physics MCQs with Solutions
Free Homi Bhabha Exam Physics Gravitation & Pressure MCQs with step-by-step solutions covering Universal Law of Gravitation, Variation in g, Mass vs Weight, Pressure & Fluid Thrust, Archimedes' Principle & Buoyancy. Practise online on Prepizo — no login needed.
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Sample questions with solutions
Q1 — Universal Law of Gravitation · hard · numerical
If the distance between two bodies is doubled, the gravitational force between them becomes:
A. double
B. one-fourth ✓ Correct
C. one-half
D. four times
Solution: Since $F \propto \dfrac{1}{r^2}$, doubling $r$ makes $F$ become $\dfrac{1}{2^2} = \dfrac{1}{4}$ of the original.
Q2 — Universal Law of Gravitation · hard · numerical
If both masses are doubled while the distance between them is kept the same, the gravitational force becomes:
A. 2 times
B. unchanged
C. 4 times ✓ Correct
D. half
Solution: $F \propto m_1 m_2$; doubling both masses multiplies the force by $2 \times 2 = 4$.
Q3 — Universal Law of Gravitation · hard · numerical
If the distance between two masses is reduced to half, the gravitational force becomes:
A. 2 times
B. 4 times ✓ Correct
C. one-fourth
D. half
Solution: $F \propto \dfrac{1}{r^2}$; halving $r$ multiplies the force by $\dfrac{1}{(1/2)^2} = 4$.
Q4 — Variation in g · hard · theory
The value of g is greatest at the:
A. top of a mountain
B. poles ✓ Correct
C. centre of the Earth
D. equator
Solution: The Earth is slightly flattened, so the poles are closer to the centre, giving a larger g than at the equator.
Q5 — Variation in g · hard · theory
The value of acceleration due to gravity at the centre of the Earth is:
A. maximum
B. zero ✓ Correct
C. equal to that at the surface
D. infinite
Solution: At the centre the mass pulls equally in all directions, so the net gravitational acceleration is zero.
Q6 — Mass vs Weight · hard · numerical
A person has a mass of 60 kg. On the Moon (where $g = 1.6$ m/s²) his weight is:
A. 96 N ✓ Correct
B. 37.5 N
C. 60 N
D. 600 N
Solution: Weight on Moon $= mg = 60 \times 1.6 = 96$ N (mass stays 60 kg).
Q7 — Mass vs Weight · hard · theory
A beam balance is used to measure mass and works the same everywhere, whereas a spring balance measures weight, because:
A. a beam balance compares masses while a spring balance responds to the force of gravity ✓ Correct
B. a spring balance measures mass directly
C. both measure the same quantity
D. a beam balance uses springs
Solution: A beam balance compares the unknown mass with standard masses (independent of g), while a spring balance reads the gravitational force (weight).
Q8 — Mass vs Weight · hard · numerical
A body weighs 490 N on Earth where $g = 9.8$ m/s². Its mass is:
A. 98 kg
B. 4802 kg
C. 490 kg
D. 50 kg ✓ Correct
Solution: Mass $= \dfrac{W}{g} = \dfrac{490}{9.8} = 50$ kg.
Q9 — Pressure & Fluid Thrust · hard · numerical
The same force is applied first over an area of 2 m² and then over 0.5 m². The pressure in the second case compared to the first is:
A. 4 times greater ✓ Correct
B. the same
C. 2 times greater
D. 4 times smaller
Solution: For a fixed force $P \propto \dfrac{1}{A}$; reducing area from 2 to 0.5 m² (a factor of 4) makes the pressure 4 times greater.
Q10 — Pressure & Fluid Thrust · hard · numerical
The pressure due to a column of water 10 m deep (density $1000$ kg/m³, $g = 10$ m/s²) is:
A. 100000 Pa ✓ Correct
B. 110000 Pa
C. 1000 Pa
D. 10000 Pa
Solution: Pressure $= h\rho g = 10 \times 1000 \times 10 = 100000$ Pa.
Q11 — Archimedes' Principle & Buoyancy · hard · numerical
A body immersed in water displaces 200 cm³ of water. The buoyant force on it (density of water $1$ g/cm³, $g = 10$ m/s²) is:
A. 0.2 N
B. 200 N
C. 2 N ✓ Correct
D. 20 N
Solution: Mass of water displaced $= 200$ g $= 0.2$ kg; buoyant force $= 0.2 \times 10 = 2$ N.
Q12 — Archimedes' Principle & Buoyancy · hard · theory
A ship made of iron floats on water although iron is denser than water because:
A. the water pushes it up with a magnetic force
B. its hollow shape makes its average density less than that of water ✓ Correct
C. iron floats on water
D. the ship has no weight
Solution: The hull encloses air, so the ship's average density is below that of water and it displaces enough water to float.
Q13 — Archimedes' Principle & Buoyancy · hard · numerical
A body weighs 50 N in air and 40 N when fully immersed in water. The buoyant force acting on it is:
A. 40 N
B. 10 N ✓ Correct
C. 90 N
D. 50 N
Solution: Buoyant force = apparent loss in weight $= 50 - 40 = 10$ N.
Q14 — Universal Law of Gravitation · medium · theory
According to Newton's universal law of gravitation, the force between two masses is:
A. directly proportional to the distance between them
B. independent of the distance between them
C. directly proportional to the product of the masses and inversely proportional to the square of the distance ✓ Correct
D. inversely proportional to the product of the masses
Solution: $F = \dfrac{G m_1 m_2}{r^2}$ — proportional to $m_1 m_2$ and inversely proportional to $r^2$.
Q15 — Universal Law of Gravitation · medium · theory
We do not notice the gravitational force of attraction between everyday objects because:
A. gravity acts only on large planets
B. friction cancels gravity
C. the gravitational constant G is extremely small ✓ Correct
D. small objects have no mass
Solution: G $\approx 6.67\times10^{-11}$ is so tiny that the force between ordinary masses is negligible.
Q16 — Universal Law of Gravitation · medium · theory
The gravitational force between two bodies is always:
A. repulsive
B. zero
C. sometimes attractive, sometimes repulsive
D. attractive ✓ Correct
Solution: Gravitation is always an attractive force between masses.
Q17 — Variation in g · medium · theory
As we go higher above the surface of the Earth, the value of acceleration due to gravity (g):
A. remains constant
B. increases
C. becomes zero immediately
D. decreases ✓ Correct
Solution: Since $g = \dfrac{GM}{r^2}$, increasing the distance $r$ from the centre decreases $g$.
Q18 — Variation in g · medium · numerical
The acceleration due to gravity on the Moon is about one-sixth of that on Earth. A body weighing 60 N on Earth weighs on the Moon about:
A. 10 N ✓ Correct
B. 60 N
C. 360 N
D. 6 N
Solution: Weight on Moon $= \dfrac{60}{6} = 10$ N.
Q19 — Variation in g · medium · theory
Two bodies of different masses are dropped together from the same height (ignoring air resistance). They:
A. the lighter one reaches first
B. reach the ground at the same time ✓ Correct
C. never reach together
D. the heavier one reaches first
Solution: g is independent of the mass of the falling body, so both accelerate equally and land together.
Q20 — Variation in g · medium · theory
The acceleration due to gravity g on a planet is given by:
A. $g = \dfrac{GM}{R}$
B. $g = GMR^2$
C. $g = \dfrac{GR}{M^2}$
D. $g = \dfrac{GM}{R^2}$ ✓ Correct
Solution: $g = \dfrac{GM}{R^2}$, where M and R are the planet's mass and radius.
Q21 — Mass vs Weight · medium · theory
Which of the following statements is correct?
A. Weight is constant but mass changes
B. Mass is constant everywhere but weight can change from place to place ✓ Correct
C. Both change from place to place
D. Both mass and weight are constant everywhere
Solution: Mass (amount of matter) is fixed, while weight $= mg$ varies as g varies.
Q22 — Mass vs Weight · medium · numerical
The weight of a 10 kg body on Earth (taking $g = 10$ m/s²) is:
A. 10 N
B. 100 N ✓ Correct
C. 1000 N
D. 1 N
Solution: Weight $= mg = 10 \times 10 = 100$ N.
Q23 — Mass vs Weight · medium · theory
The SI units of mass and weight are respectively:
A. kilogram and newton ✓ Correct
B. newton and newton
C. newton and kilogram
D. kilogram and kilogram
Solution: Mass is measured in kg; weight, being a force, is measured in newtons.
Q24 — Pressure & Fluid Thrust · medium · numerical
A force of 200 N acts normally on a surface of area 0.5 m². The pressure exerted is:
A. 100 Pa
B. 400 Pa ✓ Correct
C. 200.5 Pa
D. 40 Pa
Solution: Pressure $= \dfrac{F}{A} = \dfrac{200}{0.5} = 400$ Pa.
Q25 — Pressure & Fluid Thrust · medium · theory
A camel walks easily on soft sand because its broad feet:
A. increase the area and so reduce the pressure on the sand ✓ Correct
B. increase the force on the sand
C. decrease the area and increase pressure
D. reduce its weight
Solution: A larger contact area lowers the pressure ($P = F/A$), so the camel does not sink.
Q26 — Pressure & Fluid Thrust · medium · theory
A sharp knife cuts more easily than a blunt one because a sharp edge:
A. applies a larger force
B. has a larger area and lower pressure
C. reduces the pressure
D. has a smaller area and so produces greater pressure ✓ Correct
Solution: The small edge area concentrates the force into a high pressure, cutting more easily.
Q27 — Pressure & Fluid Thrust · medium · theory
The pressure exerted by a liquid at rest:
A. decreases with depth
B. is the same at all depths
C. is zero at the bottom
D. increases with depth ✓ Correct
Solution: Liquid pressure $= h\rho g$ increases with depth h.
Q28 — Archimedes' Principle & Buoyancy · medium · theory
Archimedes' principle states that the buoyant force on a body immersed in a fluid equals the:
A. weight of the fluid displaced by the body ✓ Correct
B. density of the fluid
C. volume of the body
D. weight of the body
Solution: The upthrust equals the weight of the fluid displaced by the submerged part of the body.
Q29 — Archimedes' Principle & Buoyancy · medium · theory
A body floats in a liquid when its weight is:
A. greater than the buoyant force
B. much greater than the buoyant force
C. equal to the buoyant force acting on it ✓ Correct
D. zero
Solution: For floating, the upward buoyant force balances the downward weight of the body.
Q30 — Archimedes' Principle & Buoyancy · medium · theory
It is easier to swim in sea water than in river water because sea water:
A. has a lower density
B. has no salt
C. has a higher density and exerts a greater buoyant force ✓ Correct
D. exerts less upthrust
Solution: Sea water is denser, so it displaces more weight per unit volume and provides greater buoyancy.