त्रिज्या के एक ठोस धात्विक अर्धगोले को पिघलाया जाता है और आधार त्रिज्या r के एक ठोस लंब वृतीय शंकु में ढाला जाता है। उनके वक्र पृष्ठीय क्षेत्रफलों का अनुपात क्या है?

This question was previously asked in
RRC Group D Previous Paper 19 (Held On: 10 Dec 2018 Shift 2)
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  1. 5/√2
  2. 2/√5
  3. 3/2
  4. 5/2

Answer (Detailed Solution Below)

Option 2 : 2/√5
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Detailed Solution

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जैसा कि हम जानते हैं,

अर्धगोला का आयतन = (2/3)πr3

शंकु का आयतन = (1/3)πr2h

प्रश्नानुसार,

(1/3)πr2h = (2/3)πr3

h = 2r

जैसा कि हम जानते हैं,

l2 = r2 + h2

⇒ l2 = r2 + (2r)2

⇒ l2 = 5r2

⇒ l = √5 r

अर्धगोला का वक्र पृष्ठीय क्षेत्रफल = 2πr2

शंकु का वक्र पृष्ठीय क्षेत्रफल = πrl = πr × (√5r) = √5r2

अपेक्षित अनुपात = 2πr2/√5πr2 = 2/√5
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