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.
Rakshitha A. R said:
4 years ago
Please explain the answer.
(1)
Ayo said:
8 years ago
I am not getting it. Please, anyone help me to understand it.
LAWRENCE said:
9 years ago
How can 3 be the radius since it's rotated?
Sangeethaa Theivendran said:
8 years ago
@ALL.
Just imagine how you draw a circle with radius 3cm using compass. Now look at the shape between two legs of compass. It is a right triangle. Now, if the right triangle is rotated a cone is formed. So radius of cone's base= base of triangle and height of both cone and triangle are same.
Just imagine how you draw a circle with radius 3cm using compass. Now look at the shape between two legs of compass. It is a right triangle. Now, if the right triangle is rotated a cone is formed. So radius of cone's base= base of triangle and height of both cone and triangle are same.
Abhinav said:
8 years ago
See in the question it is mentioned that we are rotating the side of 3cm to form cone that means the axis about which we are going to rotate is perpendicular to the side of 3cm. Hence your radius will be 3cm.
Now, just use the formula for volume of cone = 1/3 * π * r^2 * h= 1/3 *π * 9 * 4 = 12πcm^3.
Now, just use the formula for volume of cone = 1/3 * π * r^2 * h= 1/3 *π * 9 * 4 = 12πcm^3.
Lia US said:
8 years ago
Can anyone please explain me this? I didn't understand.
Sameer said:
8 years ago
I could not understand yer, please help me by explaining it.
Madhavi said:
9 years ago
We take 4 height because by using Pythagarous theorem the right angled triangle must want to satisfy the side1^2 + side2^2 =hupotenuous^2.
3^2 + 4^2 = 5^2.
25 = 25.
That's why here we take 4cm has a height.
Suppose if we take height has 5cm.
Then,
3^2 + 5^2! = 4^2.
3^2 + 4^2 = 5^2.
25 = 25.
That's why here we take 4cm has a height.
Suppose if we take height has 5cm.
Then,
3^2 + 5^2! = 4^2.
Aakriti said:
9 years ago
1. A triangle with these dimensions doesn't form a cone.
2. Even if it does then the length of the side rotated would be the circumference of the base of the figure and not the radius.
2. Even if it does then the length of the side rotated would be the circumference of the base of the figure and not the radius.
Kirti said:
9 years ago
If we rotate 3cm side won't 3cm be the circumference of its base.
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