Aptitude - Volume and Surface Area - Discussion

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"Example is better than precept."
- (Proverb)

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:

[A]. 12 cm3[B]. 15 cm3
[C]. 16 cm3[D]. 20 cm3

Answer: Option


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

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

Sachin.Nani3@Gmail.Com said: (Wed, Feb 15, 2012 07:56:22 PM)    
I could not understand, please explain any body.

Shafi said: (Fri, Mar 23, 2012 02:39:18 PM)    
Since triangle is rotated with a side of 3 hence radius=3, volume=1/3*22/7r^2h.

Vinay Vidhani said: (Sun, Jul 1, 2012 02:37:24 AM)    
We know that long side in right angle triangle is hypotenuses OK let 3 is base and 4 is a height then put the formula of volume of cone is 1/3 *pai r*r*h that's all.

Vinay Vidhani said: (Sun, Jul 1, 2012 02:39:31 AM)    
But how can we understand that 3 will base ?

Uday Kiran.M said: (Mon, Jul 9, 2012 01:37:07 PM)    
There is no need that the rotated side must be the base. You can rotate around the opposite side of triangle then also you will get the same cone.

Vidhya said: (Sat, Aug 11, 2012 08:16:57 PM)    
If the side of 3cm is rotated, won't it become the height of the cone ?

Ranjan said: (Tue, Aug 21, 2012 04:36:14 PM)    
I can't understand.

Deepika said: (Sat, Jan 12, 2013 06:03:28 PM)    
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.

Josh said: (Sun, Mar 24, 2013 09:09:34 AM)    
We take orderly the sides of triangle in required it is simply to calculate using formula 1/3*3.14*r^2*h.

Sakshi said: (Wed, May 15, 2013 05:04:14 PM)    
If it is rotated about 3 cm. How could radius be 3 cm?

Anonymous said: (Tue, Jun 4, 2013 09:46:22 PM)    
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: (Thu, Sep 26, 2013 12:18:27 PM)    
@Sakshi is right. If it is rotated about 3 cm then its radius should be 3/2 = 1.5 cm.

Laraib said: (Mon, Nov 25, 2013 11:36:58 PM)    
Tell me basics of volume and surface area.

Yasir Arafat Jubel said: (Tue, Dec 10, 2013 05:07:54 PM)    
Which mean r & h?

Gini said: (Wed, Dec 25, 2013 08:17:09 PM)    
I think 3 cm is the surface area of the circle at the base.

Then, 3 cm=22/7*r*r.

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