Aptitude - Volume and Surface Area - Discussion
Discussion Forum : Volume and Surface Area - General Questions (Q.No. 1)
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
cm315 cm3
cm316 cm3
cm320 cm3
cm3Answer: 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 2 of 8.
Anonymous said:
1 decade ago
Is the cone with base 3 rotated (form imaginary cone shape) or is it folding it (say paper) to form cone? if so how its r=3?
Silky said:
1 decade ago
@Sakshi is right. If it is rotated about 3 cm then its radius should be 3/2 = 1.5 cm.
Laraib said:
1 decade ago
Tell me basics of volume and surface area.
Yasir arafat jubel said:
1 decade ago
Which mean r & h?
Gini said:
1 decade ago
I think 3 cm is the surface area of the circle at the base.
Then, 3 cm=22/7*r*r.
Then, 3 cm=22/7*r*r.
Tony said:
1 decade ago
It can be done without knowing the formulae for the volume of a cone. Initially work out the volume of a cylinder with base 3cm and height 4 cm. The volume swept through rotation for the cylinder would be 113.04 cubic cm. Now visualize how many cones it would take to sweep the same volume as the cylinder (it is 3 - one above inverted and 1 side on 90 degrees). Divide 113.04 by 3 which gives the correct answer.
Pritam said:
1 decade ago
Why should the base be taken as 3? why can't it be 4? what's the logic?
Pintu said:
1 decade ago
It is not mentioned that it is rotated with 3 cm it can be rotated about 3 cm, then in that case 3cm will be the height and 4 cm will be the radius.
Asim said:
1 decade ago
If the question says the triangle is rotated keeping side of 3 cm fixed then the side of 3cm will be the height and 4 cm will be the radius.
Ankush said:
1 decade ago
If the cone is made by rotating the side which is 3 then 3 will become the circumference of the base being 2pie r. Hence 2pie r = 3 and r = 3/2pie.
Is it correct?
Is it correct?
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