# F.3 Maths

An inverted frustum with a depth of 7 cm. The radii of the top and bottom are 4 cm and 3 cm respectively.

a) Find,in terms of Π, the volume of the frustum.

b) If the frustum is filling with water at a speed of 15 cm3 per second, how much time is required to fill the frustum?

個ans係 a) (259Π/3) cm3

b) 19 s

詳細steps plz..

### 1 Answer

- Brian LuiLv 51 decade agoFavorite Answer
The height of the removed portion of the cone = h cm

h : (h+7) = 3 : 4

h = 21

The height of the complete cone = 21 + 7 = 28 cm

(a)

Volume of frustum

= ⅓π(4)²(28) - ⅓π(3)²(21)

= 259π/3 cm3

(b)

Time required

= (259π/3) / 15

≈ 18.1 seconds

2007-03-11 22:35:22 補充：

For (b), if it is to be rounded up to the next complete second, then it is 19 seconds.

2007-03-11 22:35:32 補充：

For (b), if it is to be rounded-up to the next complete second, then it is 19 seconds.