Question 78

A solid sphere of diameter 7 cm is cut into two equal halves. What will be the increase (in cm2) in the total surface area ?

Solution

A solid sphere when cut into two equal halves, two solid hemispheres will be formed

Radius of sphere = $$\frac{7}{2}$$ cm

Increase in total surface area = $$(2\times3\pi r^2)-(4\pi r^2)$$

= $$6\pi r^2-4\pi r^2=2\pi r^2$$

= $$2\times\frac{22}{7}\times(\frac{7}{2})^2$$

= $$11\times7=77$$ $$cm^2$$

=> Ans - (A)

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