Question

6. In a cylinder, if radius is halved and height is doubled, then find its volume.
7. 60 circular plates, each of radius 7 cm and thickness one-third of a cm, are placed one above another to form a solid circula
cylinder. Find the total surface area and the volume of the cylinder so formed.
8. A sphere and a right circular cylinder of the same radius have equal volumes. By what percentage does the
[NCERT Exemplar]​

Answer 1

6) Let initial radius = r

& initial height = h

Initial volume = v = πr²h

Now,

New radius ,r' = r/2

New height, h' = 2h

New volume, v' = πr'²h'

→ v' = π(r/2)²(2h)

→ v' = 2πr²h/4

→ v' = πr²h/2

→ v' = v/2 _______________(Ans.)

7) radius of each plate, r = 7cm

& thickness of each plate, t = 1/3 cm

Now, height of cylinder formed by 60 plates = 60 x t = 60 x 1/3 = 20cm

So, h = 20cm

Hence, Total surface area of cylinder

= 2πr(r + h)

= 2π x 7(7 + 20)

= 14π(27)

= 378π

= 1187.522 cm² ______________(Ans.)

8) Sorry, but your last question is incomplete...??