Aptitude  Volume and Surface Area  Discussion
Discussion Forum : Volume and Surface Area  General Questions (Q.No. 5)
5.
A hollow iron pipe is 21 cm long and its external diameter is 8 cm. If the thickness of the pipe is 1 cm and iron weighs 8 g/cm^{3}, then the weight of the pipe is:
Answer: Option
Explanation:
External radius = 4 cm,
Internal radius = 3 cm.
Volume of iron 




= 462 cm^{3}. 
Weight of iron = (462 x 8) gm = 3696 gm = 3.696 kg.
Discussion:
60 comments Page 1 of 6.
Debosmita Misra said:
12 months ago
The external Diameter is given 8 cm and the thickness of the pipe is given 1 cm.
Hence, the External radius (R) would be 4 cm & Internal radius(r) would be (8  1  1)/2 = 3cm.
And the volume will be PI*(R*R  r*r)*h = (22/7)*(4*4  3*3)*21 = (22/7)*(169)*21 = 462 g.
Therefore, weight of the pipe = (462*8) g = 3696 g = 3.696 kg.
Hence, the External radius (R) would be 4 cm & Internal radius(r) would be (8  1  1)/2 = 3cm.
And the volume will be PI*(R*R  r*r)*h = (22/7)*(4*4  3*3)*21 = (22/7)*(169)*21 = 462 g.
Therefore, weight of the pipe = (462*8) g = 3696 g = 3.696 kg.
Bala said:
1 year ago
@Dinesh.
Thank You for your good explanation.
Thank You for your good explanation.
Dinesh Reddy said:
2 years ago
Can anyone explain this answer once again deeply?
Pema said:
3 years ago
Why cant it be =pi * 3^2 * 21?
Ram said:
3 years ago
External diameter = 8 cm.
External radius = R =4 cm.
Given Thickness= 1 cm.
So, internal diameter= (81) cm = 7 cm.
Internal radius = r = 3.5 cm not 3 cms.
According to the volume of iron;
= 21*(22/7)*(1612.25),
= 247.5 cm3.
Weight of iron = 247.5 * 8 = 1980 gram or 1.98 kg.
External radius = R =4 cm.
Given Thickness= 1 cm.
So, internal diameter= (81) cm = 7 cm.
Internal radius = r = 3.5 cm not 3 cms.
According to the volume of iron;
= 21*(22/7)*(1612.25),
= 247.5 cm3.
Weight of iron = 247.5 * 8 = 1980 gram or 1.98 kg.
(2)
Roney said:
4 years ago
@Nazim.
From both side the 1cm will be deducted.
so dia = 6cm radius 3cm.
From both side the 1cm will be deducted.
so dia = 6cm radius 3cm.
(2)
Nazim Shaik K said:
4 years ago
External diameter = 8 cm.
External radius = R =4 cm.
Given Thickness= 1 cm.
So, internal diameter= (81) cm = 7 cm.
Internal radius = r = 3.5 cm not 3 cms.
According to the volume of iron;
= 21*(22/7)*(1612.25),
= 247.5 cm3.
Weight of iron = 247.5* 8 = 1980 gram or 1.98 kg.
External radius = R =4 cm.
Given Thickness= 1 cm.
So, internal diameter= (81) cm = 7 cm.
Internal radius = r = 3.5 cm not 3 cms.
According to the volume of iron;
= 21*(22/7)*(1612.25),
= 247.5 cm3.
Weight of iron = 247.5* 8 = 1980 gram or 1.98 kg.
(1)
Sunil said:
4 years ago
Why 4 square minus 3 square equals to 7 * 1.
Rahul said:
5 years ago
There is a formula for hollow sphere 3.14 (R^2r^2)h.
CHINMAYE said:
6 years ago
@Rohan.
It's given in the question that iron weighs 8 g/cm3. It's nothing but a density.
It's given in the question that iron weighs 8 g/cm3. It's nothing but a density.
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