Archimedes' Principle & Buoyancy — Homi Bhabha Class 9 Physics MCQs with Solutions
Free Homi Bhabha Class 9 Physics Archimedes' Principle & Buoyancy MCQs with step-by-step solutions (10 questions). Part of Gravitation & Pressure. Practise online on Prepizo — no login needed.
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Questions with solutions
Q1 — 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.
Q2 — 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.
Q3 — 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.
Q4 — 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.
Q5 — 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.
Q6 — 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.
Q7 — Archimedes' Principle & Buoyancy · easy · theory
The upward force exerted by a fluid on an object placed in it is called:
A. gravitational pull
B. thrust
C. buoyant force (upthrust) ✓ Correct
D. pressure
Solution: The upward force a fluid exerts on a body placed in it is the buoyant force, also called upthrust.
Q8 — Archimedes' Principle & Buoyancy · easy · theory
An object floats on the surface of a liquid when:
A. its weight is greater than the buoyant force
B. its weight equals the buoyant force acting on it ✓ Correct
C. its weight is much greater than the upthrust
D. it loses all its weight
Solution: A body floats when the upward buoyant force balances its weight, so weight = buoyant force.
Q9 — Archimedes' Principle & Buoyancy · medium · numerical
A body weighs 50 N in air and 40 N when it is fully immersed in water. The buoyant force acting on the body is:
A. 90 N
B. 40 N
C. 50 N
D. 10 N ✓ Correct
Solution: The apparent loss in weight equals the buoyant force. Buoyant force = 50 - 40 = 10 N.
Q10 — Archimedes' Principle & Buoyancy · hard · numerical
A block of volume 500 cm³ is fully immersed in water (density 1000 kg/m³, g = 10 m/s²). The buoyant force on it is:
A. 0.5 N
B. 5 N ✓ Correct
C. 50 N
D. 500 N
Solution: Buoyant force = density × volume × g = 1000 × (500×10⁻⁶) × 10 = 1000 × 0.0005 × 10 = 5 N.