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General ScienceMediumAsked in: CDS · CDS-II 2017, GK

A person is standing on a frictionless horizontal ground. How can he move by a certain distance on this ground?

  1. A.By sneezing
  2. B.By jumping
  3. C.By running
  4. D.By rolling

Correct answer

A. By sneezing

Explanation

The correct answer is A, By sneezing. On a frictionless surface the person can move only by throwing something out in one direction, and a sneeze pushes air forward so the body recoils backward.

Walking, running and rolling all need friction: the foot or body pushes back on the ground, and the ground's frictional force pushes the person forward. Without friction there is no such external horizontal force. The law of conservation of momentum then decides the matter. If the person blows air or throws any object one way, the system's total momentum stays zero, so the body gains an equal and opposite momentum and slides away. This is the same principle as a gun's recoil or a rocket's thrust.

B is wrong because a jump straight up only lifts the person, who lands at the same spot, and a sideways push needs friction. C is wrong because running depends on pushing against the ground through friction. D is wrong because rolling also needs friction at the point of contact.

Exam tip: no friction means no walking; motion comes only from recoil, by conservation of momentum, as in rockets and guns.

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.