When a body falls freely under gravity, its MCQ with Answer and Explanation

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When a body falls freely under gravity, its

A. Mass increases

B. K.E. decreases

C. Mechanical energy remains constant

D. P.E. increases

Answer: Option C

Solution (By JKSSB Mock Tests)

Neglecting air resistance, total mechanical energy conserved.

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Question #1

Who proposed the theory of relativity?

A. Maxwell

B. Einstein

C. Galileo

D. Newton

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Correct Answer: Option B

Explanation:
Albert Einstein proposed special relativity (1905) and general relativity (1915).

This question belongs to: Science Physics

Question #2

A radioactive substance has half-life of 10 days. Fraction remaining after 30 days is

A. 1/16

B. 1/2

C. 1/4

D. 1/8

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Correct Answer: Option D

Explanation:
Number of half-lives = 30/10 = 3. Remaining = (1/2)³ = 1/8. Exponential decay N = N₀(1/2)^(t/T). Radioactive decay constant λ = ln2/T.

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Question #3

Heat required to raise 2 kg water from 20°C to 100°C: (c_water = 4200 J/kg·K)

A. 168 kJ

B. 336 kJ

C. 672 kJ

D. 840 kJ

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Correct Answer: Option C

Explanation:
Q = mcΔT = 2×4200×(100-20) = 2×4200×80 = 672000 J = 672 kJ. Direct calorimetry formula application. Memory tip: 'Q = mcΔT; ΔT in Celsius or Kelvin same'. Basic numerical testing specific heat concept, frequently appearing in thermodynamics sections of competitive exams.

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