A right circular cylinder has height 21cm and radius 7cm. The cylinder is cut into three equal parts parallel to the base. What is the increase in total surface area?
Answer & explanation
Correct answer: option 1
T.S.A. of bigger cylinder = 2\(\pi \)rH + 2\(\pi \)r2........(i)
T.S.A. of 3 parts = 3 × (2\(\pi \)rh + 2\(\pi \)r2)
= 2\(\pi \)rH + 6\(\pi \)r2 ..........(ii) (∵3h = H)
⇒ Increase is (ii) - (i),
⇒ 4\(\pi \)r2 = 4 × \(\frac{22}{7}\) × 7 × 7 = 616 cm2