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Aptitude - Volume and Surface Area - Discussion

Discussion Forum : Volume and Surface Area - General Questions (Q.No. 1)
Volume and Surface Area
1.
A right triangle with sides 3 cm, 4 cm and 5 cm is rotated the side of 3 cm to form a cone. The volume of the cone so formed is:
12 cm3
15 cm3
16 cm3
20 cm3
Answer: Option
Explanation:

Clearly, we have r = 3 cm and h = 4 cm.

Volume = 1 r2h = 1 x x 32 x 4 cm3 = 12 cm3.
3 3

Video Explanation: https://youtu.be/Njsid2mVwUY

Discussion:
77 comments Page 4 of 8.
Rama said:   10 years ago
Since triangle is rotated with side of 3 cm hence radius is 3.

Clearly, we have v-1/3*r*r*h.
V!CKY said:   10 years ago
@Sakshi and other who doubt in radius @ read question carefully.

i.e rotated the side of 3 cm to form a cone.

Diameter = 2*Radius.
Tina said:   10 years ago
If 3 cm side is rotated, shouldn't it form circumference of cone?

Then 2*pie*r = 3.

How can r itself be 3 here?
Suhail said:   10 years ago
Dear friend,

As it is moved along the side 3 cm hence this 3 cm will be distributed entire circumference.

So 3 = 2*22/7*r.

r = 3/2Π.
Srikanth said:   10 years ago
Volume of cone is (1/3)*pi*r*r*h = (1/3)*(22/7)*3*3*4 then, the value will be 12(22/7)cm^3.
Aashish said:   10 years ago
We can take 4 as base. And according to which volume will be 16*pi or remove 16*pi from the options.

Or we can have only one correct option either 12pi or 16pi.
Shinu said:   9 years ago
Pi factor should be included.
Archana said:   9 years ago
How you take 3cm for the base?

Please, Explain.
Mia khalifa said:   9 years ago
Why the 3 cm is taken as the radius?
LAWRENCE said:   9 years ago
How can 3 be the radius since it's rotated?
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