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.
Ram said:
2 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)
Dhinesh said:
6 years ago
Because, the VOLUME OF HOLLOW CYLINDER FORMULA is π(R^2r^2)h.
Assume, (hollow iron pipe is in the shape of a hollow cylinder).
Here, we require RADIUS, but in question, it is in DIAMETER.
Outer dia=8cm[R=d/2=4cm];;then thickness=1cm(I.e, reduce diameter Of outer pipe by 2cm)..since thickness is both sides of pipe..(thickness = 1+1)
This gives diameter Of inner pipe = 6cm[r=d/2=3cm].
Then substitute R&r in formula....
Volume = 22/7 * (4^2  3^2) * 21 = 22 * (16  9) * 3 = 22*(7)*3 = 462 cm3.
Weight = density * volume.
= 8 * 462 = 3696 g.
= 3696/1000 = 3.696 kg.
Assume, (hollow iron pipe is in the shape of a hollow cylinder).
Here, we require RADIUS, but in question, it is in DIAMETER.
Outer dia=8cm[R=d/2=4cm];;then thickness=1cm(I.e, reduce diameter Of outer pipe by 2cm)..since thickness is both sides of pipe..(thickness = 1+1)
This gives diameter Of inner pipe = 6cm[r=d/2=3cm].
Then substitute R&r in formula....
Volume = 22/7 * (4^2  3^2) * 21 = 22 * (16  9) * 3 = 22*(7)*3 = 462 cm3.
Weight = density * volume.
= 8 * 462 = 3696 g.
= 3696/1000 = 3.696 kg.
(1)
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)
Ravi said:
7 years ago
Surface area of iron cube of side 10cm is?
Dhana reddy said:
6 years ago
Why 4^2 3^2? Please explain this step.
Indranath said:
6 years ago
Why not (43)^2?
Gautam said:
6 years ago
Isn't weight=mass*gravity?
Ajay said:
6 years ago
Could you explain me about pi?
Utham said:
6 years ago
The Internal radius and external radius. given is 8g/cm^3 not for hollow space.So, the first find out the full volume that is with the use of external radius. Now subtract hollow space that volume with internal radius. R^2h*r^2h.
Post your comments here:
Quick links
Quantitative Aptitude
Verbal (English)
Reasoning
Programming
Interview
Placement Papers