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Question

I take a flat metallic circular plate of radius r. Now by hammering it I now convert it into a metallic hemisphere of same radius as circular plate. What is the change in surface area of the metal due to the hammering?


A

2πr2

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B

3πr2

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C

4πr2

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D

πr2

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Solution

The correct option is A

2πr2


A flat horizontal metal plate consists of 2 sides both circular and having same area.

The area of one side of circular plate= πr2

Since there are 2 sides, area = 2πr2

A metallic hemisphere also consists of 2 sides. Each side has same area.

Area of one hemispherical plate = 2πr2

Since there are 2 sides area = 4πr2

Change in surface area between plate and sphere = 4πr2 - 2πr2 = 2πr2


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