The half-life of a radioactive substance is 10 days. After 30 days, the fraction decayed is MCQ with Answer and Explanation

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The half-life of a radioactive substance is 10 days. After 30 days, the fraction decayed is

A. 2/3

B. 1/3

C. 7/8

D. 1/8

Answer: Option C

Solution (By JKSSB Mock Tests)

3 half-lives, remaining = 1/8, decayed = 7/8.

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Question #1

In SHM, the restoring force is proportional to

A. Velocity

B. Displacement

C. Square of displacement

D. Time

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Correct Answer: Option B

Explanation:
F ∝ -x, defining SHM.

This question belongs to: Science Physics

Question #2

If a force of 10 N acts on a body and displaces it by 2 m in the direction of the force, the work done is:

A. 12 J

B. 0 J

C. 20 J

D. 5 J

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Correct Answer: Option C

Explanation:
Work done (W) is calculated as the dot product of force and displacement: W = F × d × cos(θ). Since the displacement is in the direction of the force, the angle θ is 0°, and cos(0°) = 1. W = 10 N × 2 m × 1 = 20 Joules (J).

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Question #3

An object is placed at 2F of a convex lens. Image formed is

A. Virtual, inverted, same size

B. Real, inverted, same size

C. Virtual, erect, magnified

D. Real, inverted, diminished

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Correct Answer: Option B

Explanation:
At 2F, image also at 2F, real inverted same size. Used in photocopiers.

This question belongs to: Science Physics

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