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UPSC 2000: Assertion (A): A man standing on a completely frictionless surface can propel himself by whistling. Reason (R): If no external force acts on a system, its momentum cannot change.
(a)Both A and R are true, and R is the correct explanation of A
(b)Both A and R are true, but R is not a correct explanation of A
(c)A is true, but R is false
(d)A is false, but R is true
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Not attemptedCorrect Answer: (a) Both A and R are true, and R is the correct explanation of A
Assertion is true: on a friction-free surface a man can move by expelling air while whistling; the backward momentum of the air imparts equal and opposite momentum to his body. Reason is also true and is the precise principle explaining the assertion—the total momentum of an isolated system (man + air) remains constant when no external force acts. ([licchavilyceum.com](https://licchavilyceum.com/upsc-civil-services-prelims-2000-solved-question-paper/))
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Frequently Asked Questions
What is the correct answer to this UPSC 2000 Science & Technology question?▼
The correct answer is option (a): Both A and R are true, and R is the correct explanation of A. Watch the detailed video explanation in our Sherlocking Prelims course on UnlockIAS.
Which year was this Physics question asked in UPSC Prelims?▼
This question was asked in UPSC CSE Prelims 2000, GS Paper 1, as Question 103. It falls under Science & Technology > Physics.
What is the difficulty level of this UPSC question?▼
This question is rated "moderate". It requires sound conceptual understanding of the topic.
How many UPSC Prelims questions have been asked from Physics?▼
UPSC has asked 104 questions from Physics (under Science & Technology) across multiple years. Visit the topic page to see the full list and year-wise trends.