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Question
A golf ball has diameter equal to 4.2 cm. Its surface has 200 dimples each of radius 2 mm. Calculate the total surface area which is exposed to the surroundings assuming that the dimples are hemispherical.
Solution
Surface area of ball
`=4pir^2`
`=4pi (4.2 /2)^2`
`= 17.64 pi cm^2`
Total surface area exposed
SA of ball `- 200 (pir^2 - (4pir^2)/2)`
`=17.64 pi - 200 pir^2`
`=17.64 pi -8pi`
`= 80.5 cm^2`
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