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General ScienceMediumAsked in: CDS · CDS-I 2025, GK

A metallic sphere of mass 1 kg and volume 2 × 10⁻⁴ m³ is completely immersed in water. The buoyant force exerted by water on the sphere is : (Given : density of water = 1000 kg/m³, g = 10 m/s²)

  1. A.0.5 N
  2. B.1.5 N
  3. C.2 N
  4. D.2.5 N

Correct answer

C. 2 N

Explanation

The correct answer is C, 2 N. By Archimedes' principle, the buoyant force equals the weight of the water displaced by the sphere.

A fully immersed body displaces its own volume of water, here 2 × 10⁻⁴ m³. The mass of that water is density × volume = 1000 × 2 × 10⁻⁴ = 0.2 kg, and its weight is 0.2 × 10 = 2 N. So the upward push is 2 N. The mass of the sphere (1 kg) does not enter the calculation at all; it only decides whether the sphere sinks. Its weight is 10 N, far more than 2 N, so the metal sphere sinks while still feeling a 2 N upthrust.

A, 0.5 N, and B, 1.5 N, are less than the weight of the displaced water. D, 2.5 N, is more than it; none of these matches density × volume × g.

Exam tip: buoyant force = ρ × V × g of the fluid; the body's own mass only decides sinking or floating.

Practice Questions

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Q1.General ScienceAsked in: UPSC Civil Services · CSE Prelims 2022, GS Paper IMedium

Which of the following are nitrogen-fixing plants?

1. Alfalfa

2. Amaranth

3. Chickpea

4. Clover

5. Purslane (Kulfa)

6. Spinach

Select the correct answer using the code given below:

  1. A.1, 3 and 4 only
  2. B.1, 3, 5 and 6 only
  3. C.2, 4, 5 and 6 only
  4. D.1, 2, 4, 5 and 6
Show answer
Correct answer: A. 1, 3 and 4 only

Alfalfa, chickpea and clover are legumes, and legumes fix nitrogen. Plants of the legume family (Fabaceae) carry root nodules that house Rhizobium bacteria.

Q2.General ScienceAsked in: UPSC CAPF · CAPF 2017, Paper IMedium

The mass number of an element is NOT changed when it emits

  1. A.Alpha and Beta radiations only
  2. B.Alpha and Gamma radiations only
  3. C.Beta and Gamma radiations only
  4. D.Alpha, Beta and Gamma radiations
Show answer
Correct answer: C. Beta and Gamma radiations only

Neither beta nor gamma emission changes the total number of protons and neutrons in a nucleus, so the mass number stays the same.

Q3.General ScienceAsked in: UPSC CAPF · CAPF 2025, Paper IMedium

Which one among the following statements about facilitated transport in plants is correct?

  1. A.All passive transports are types of facilitated transport.
  2. B.Facilitated transport is an example of active transport.
  3. C.Water moves across plasma membrane by active transport.
  4. D.Facilitated transport requires assistance of carrier proteins.
Show answer
Correct answer: D. Facilitated transport requires assistance of carrier proteins.

In facilitated transport, molecules cross the membrane with the help of membrane proteins, while still moving down their concentration gradient.

Q4.General ScienceAsked in: UPSC CAPF · CAPF 2017, Paper IMedium

Who among the following has coined the term 'Quark', the fundamental particles that make up protons and neutrons in an atomic nucleus ?

  1. A.Richard Feynman
  2. B.Murray Gell-Mann
  3. C.Albert Einstein
  4. D.Niels Bohr
Show answer
Correct answer: B. Murray Gell-Mann

The American physicist Murray Gell-Mann proposed quarks in 1964 and gave them their name. Gell-Mann, and independently George Zweig, suggested that protons, neutrons and other such particles are built from smaller units.