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 7 of 8.
Pritam said:
1 decade ago
Why should the base be taken as 3? why can't it be 4? what's the logic?
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.
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.
Yasir arafat jubel said:
1 decade ago
Which mean r & h?
Laraib said:
1 decade ago
Tell me basics of volume and surface area.
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.
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?
Sakshi said:
1 decade ago
If it is rotated about 3 cm. How could radius be 3 cm?
Josh said:
1 decade ago
We take orderly the sides of triangle in required it is simply to calculate using formula 1/3*3.14*r^2*h.
Deepika said:
1 decade ago
We know long side is hypotenuse according to question which will be 5cm then height is 4cm & base is 3cm then we extent the 3cm behind 4cm height as a diameter & draw the circle along this & calculate the volume from formula.
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