Assertion (A): It is easier to pull a lawn roller than to push it. Reason (R): Pushing increases the apparent weight of the roller, thereby increasing the frictional force. MCQ with Answer and Explanation

Assertion (A): It is easier to pull a lawn roller than to push it. Reason (R): Pushing increases the apparent weight of the roller, thereby increasing the frictional force.
A. Both A and R are true but R is NOT the correct explanation of A.
B. Both A and R are true and R is the correct explanation of A.
C. A is true but R is false.
D. A is false but R is true.
Answer: Option B
Solution (By JKSSB Mock Tests)
When you pull a roller at an upward angle, the vertical component of the applied force acts strictly upwards, reducing the normal reaction (N = mg - Fsin_theta) and thus reducing friction (muN). When you push it at a downward angle, the vertical component adds to the weight (N = mg + Fsin_theta), increasing the normal reaction and consequently increasing the rolling friction.

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Question #1
The time taken for a radioactive sample to decay to 1/16th of its initial activity is:
A. 8 half-lives
B. 3 half-lives
C. 4 half-lives
D. 2 half-lives

Correct Answer: Option C


Explanation:
After n half-lives, activity reduces to (1/2)ⁿ of initial. Set (1/2)ⁿ = 1/16 ⇒ (1/2)ⁿ = (1/2)⁴ ⇒ n = 4 half-lives. Thus time = 4 × half-life. Memory aid: '1/2ⁿ remaining after n half-lives; 1/16 = 1/2⁴ ⇒ 4 half-lives'. This radioactivity calculation is frequently tested in competitive exams. Always express fraction as power of 1/2 to find half-life count. This problem assesses understanding of exponential decay without heavy computation.

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The power of a lens is measured in
A. Metre
B. Dioptre
C. Watt
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Correct Answer: Option B


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Dioptre (D) = m⁻¹. Power = 1/f in metres. Convex positive, concave negative. Optometry uses dioptre.

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A electric iron of 500 W is used for 2 hours. Energy consumed in kWh is
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B. 0.5 kWh
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D. 1 kWh

Correct Answer: Option D


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