Question

A 20m deep well with diameter 7m is dug and the earth digging is evenly spread out to form a platform 22m by 14m.Find the height of the platform

Answer 1

Answer:

the correct answer is 2.5 m

Step-by-step explanation:

please refer the image..

Answer 2

Given:-

• Depth (h) of well = 20m.
• Radius (r) of circular end of well = 7/2 m.

To find:-

• Find the height of platform is ?

Solutions:-

• Let height of the platform = h

Area of platform = length × breadth

=> 22 × 14

=> 308m²

Volume of soil dug from the well will be equal to the volume of soil scattered on the platform.

Volume of soil from well = Volume of soil used to makes sure platform.

=> πr²h = Area of platform × height of platform

=> π × (7/2)² × 308 × h

=> π × 49/4 × 20 = 308 × h

=>h = 22/7 × 49/4 × 20/308

=> h = 11 × 7/2 × 10/154

=> h = 77/2 × 10/154

=> h = 10/4

=> h = 5/2

=> h = 2.5m

Hence, the height of platform is 2.5m.

Some Important:-

• Volume of cylinder ( Area of base × height ). = (πr²) × h

= πr²h

• Curved surface = ( Perimeter of base ) × height.

= (2πr) × h

= 2πrh

• Total surface are = Area of circular ends + curved surface area.

= 2πr² + 2πrh

= 2πr(r + h)

Where,

• r = radius of the circular base of the cylinder.
• h = height of cylinder.