A solid problem

Geometry Level 3

A cylindrical glass is made up of steel whose internal radius is 7 cm and external radius is14 cm and and height is 10cm,then find its volume in cubic centimetre. (assuming the glass is uniform and the width of steel is same everywhere)

440 3080 4620 5698

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2 solutions

Volume of the base = π × 1 4 2 × 7 = 4312 =π\times 14^2\times 7=4312 c. c. assuming the value of π π to be 22 7 \dfrac {22}{7} .

Height of side wall is 10 7 = 3 10-7=3 cm. So it's volume is π × ( 1 4 2 7 2 ) × 3 = 1386 π\times (14^2-7^2)\times 3=1386 c. c.

So the volume of the material of the container is 4312 + 1386 = 5698 4312+1386=\boxed {5698} c. c.

First method: The glass can be broken into a hollow cylinder (of internal radius 7cm ,external radius 14cm and height 10 cm ) and a solid cylinder (of radius 7cm and height 7cm).Intution behind it,if you think about a glass we can cut out it into a hollow cylinder by pushing its base outside and since width remains every where so, height comes out 7cm(R-r=14-7)....now the total volume of glass comes out volume of hollow cylinder + volume of solid base = 4620+1078=5698 cubic centimetre.......... Second method: The glass can be broken into a hollow cylinder (of internal radius 7cm ,external radius 14cm and height 3cm[10-(R-r)] ) and a solid cylinder (of radius 14cm and height 7cm).Intution behind it you can cut out solid base from glass So,volume of glass= volume of hollow cylinder+ solid base=4312+1386=5698...end game

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