Question
A copper wire of length 36 m and diameter 2 mm is melted to form a sphere. The radius of the sphere (in cm) is :
Answer: Option B
Let the radius of the sphere be r cm
Then,
$$\eqalign{
& \frac{4}{3}\pi {r^3} = \pi \times {\left( {0.1} \right)^2} \times 3600 \cr
& \Leftrightarrow {r^3} = 36 \times \frac{3}{4} \cr
& \Leftrightarrow {r^3} = 27 \cr
& \Leftrightarrow r = 3\,cm \cr} $$
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Let the radius of the sphere be r cm
Then,
$$\eqalign{
& \frac{4}{3}\pi {r^3} = \pi \times {\left( {0.1} \right)^2} \times 3600 \cr
& \Leftrightarrow {r^3} = 36 \times \frac{3}{4} \cr
& \Leftrightarrow {r^3} = 27 \cr
& \Leftrightarrow r = 3\,cm \cr} $$
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