Sphere to wire !!!!

Geometry Level 2

A copper sphere of diameter 18 cm is drawn into a wire of diameter 4 mm. Find the length of the wire.(in meters )


The answer is 243.

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14 solutions

Prasun Biswas
Dec 25, 2013

We know that when any solid is melted or drawn and given a new shape, the volume remains the same as before.

Let l l be the length of the wire.

So, volume of the sphere in metres = 4 3 π r 3 = 4 3 π ( 18 2 × 100 ) 3 =\frac{4}{3} \pi r^{3} = \frac{4}{3} \pi (\frac{18}{2\times 100})^3

Now, after being drawn into wire, its volume in metres = π r 2 l = π ( 4 2 × 1000 ) 2 l =\pi r^{2} l= \pi (\frac{4}{2\times 1000})^2 l

Now, we have 4 3 π ( 18 2 × 100 ) 3 = π ( 4 2 × 1000 ) 2 l \frac{4}{3} \pi (\frac{18}{2\times 100})^3=\pi (\frac{4}{2\times 1000})^2 l

4 3 π × 18 200 × 18 200 × 18 200 = π × 4 2000 × 4 2000 l \implies \frac{4}{3} \pi \times \frac{18}{200} \times \frac{18}{200} \times \frac{18}{200}=\pi \times \frac{4}{2000} \times \frac{4}{2000} l

On evaluating, we finally get, l = 9 × 3 × 9 = 243 l=9\times 3\times 9 = \boxed{243}

So, we get the length of the wire = l = 243 =l=\boxed{243}

Vishal Yash
Jul 12, 2014

volume of sphere = volume of wire

Volume of sphere= 4/3 πR^3, Volume of cylinder= πr^2 h, When a sphere is turned into a wire then the wire act like a cylinder. So here we have radius of sphere,R = 18/2=9 cm Radius of wire, r = 4/2=2 mm= 0.2 cm So , volume of sphere= Volume of cylinder Or, 4/3 πR^3 = πr^2 h Or, 4/3 π〖(9)〗^3 = π〖(0.2)〗^2 h Or, h= 243 m

Bikash Kumar
Feb 26, 2014

vol. of sphere=vol. of cylinder; 4/3(pi)r^3=pi(R^2)h ; where, r=radius of the sphere,r=radius of sphere & h=height of the cylinder i.e,length of the wire 4/3(3.14)(0.09^3)=(3.14)(0.002^2)h so,h=4/3(3.14)(0.09^3)/(3.14)(0.002^2 ) hence,h=243m(sol.)

Dilbwag Singh
Feb 5, 2014

We know the volume of a sphere is 4/3x22/7xr^3. Therefore the volume of the given sphere is 21384/7. Now the wire is in the form of a cylinder so volume of a cylinder is 22/7xr^2xh. So by the problem 22/7xr^2xh=21384/7. So by solving the equation we get h=243 meters.

Henry Okafor
Jan 19, 2014

The volume of a sphere is 4 3 \frac{4}{3} \ * pi * r * r* r ) = 4 3 \frac{4}{3} * pi * 0.09 * 0.09 * 0.09 = 0.000972 pi.

The volume of a cylinder is pi * r * r * h = pi * 0.002 * 0.002 * h = 0.000004h * pi.

Since they are from the same materials, they have the same volume.

Thus, 0.000972 pi = 0.000004h * pi. h = 0.000972 0.000004 \frac{0.000972}{0.000004} = 243m

Tan Li Xuan
Jan 7, 2014

The formula for the volume of a sphere is 4 3 π r 3 \frac{4}{3}\pi r^{3} .The problem gives us the diameter of the sphere.The radius of the sphere is equal to half of the diameter so r = 18 c m 2 = 9 c m r = \frac{18 cm}{2} = 9 cm .So the volume of the copper sphere is 4 3 × π × 9 c m × 9 c m × 9 c m = 972 π c m 3 \frac{4}{3} \times \pi \times 9 cm \times 9 cm \times 9 cm = 972\pi cm^{3} .

The formula for the volume of a cylinder is h π r 2 h\pi r^{2} where h h is the height( in this case the length) of the cylinder and r r is the radius of the base.The radius of the copper wire is 0.4 c m 2 = 0.2 c m \frac{0.4 cm}{2} = 0.2 cm .So the volume of the wire is h π 0.04 c m 2 h\pi 0.04 cm^{2} .

Because the entire copper sphere is drawn into the wire,the volume of the sphere must be equal to the volume of the wire.So we get

972 π c m 3 = h π 0.04 c m 2 972\pi cm^{3} = h\pi 0.04 cm^{2}

Now we divide both sides by π \pi .We get

972 c m 3 = 0.04 h c m 2 972 cm^{3} = 0.04h cm^{2}

Then we divide both sides by 0.04 c m 2 0.04 cm^{2} and we get

24300 c m = h 24300 cm = h

So h = 24300 c m h = 24300 cm .But the question is asking for the length in meters,so we convert 24300 c m 24300 cm to meters and we get 24300 c m 100 c m = 243 m \frac{24300 cm}{100 cm} = 243 m .So the answer is 243 m \boxed{243 m} .

Ashutosh Krishna
Dec 26, 2013

VOLUME OF SPHERE=4/3 X 22/7 X R^3

VOLUME OF WIRE(VOLUME OF CYLINDER)=22/7 X r^2 X H

VOLUME OF SPHERE=VOLUME OF CYLINDER

4/3 X 22/7 X R^3=22/7 X r^2 X H

4/3 X 9 X 9 X 9=2/10 X 2/10 X H

24300 CM=H

243 METERS=H

Ajay Yadav
Dec 25, 2013

volume will remain constant & hence volume of sphere = volume of wire(cylinder)

Even surface area will remain constant right??

Vasavi GS - 7 years, 5 months ago

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need not

Nuthan Prasanna - 7 years, 5 months ago
Lim Zi Heng
Dec 25, 2013

Volume of sphere = 4 3 π r 3 \frac{4}{3}\pi r^3

Volume of cylinder = π r 2 h \pi r^2h

4 3 π r 3 \frac{4}{3}\pi r^3 = π r 2 h \pi r^2h

4 3 π ( 0.09 ) 3 \frac{4}{3}\pi (0.09)^3 = π ( 0.002 ) 2 h \pi (0.002)^2h

Divide the π \pi of that equation

4 3 × 0.000729 \frac{4}{3} \times 0.000729 = 0.000004 × h 0.000004 \times h

h = 4 3 × 0.000729 0.000004 h = \frac {\frac{4}{3} \times 0.000729}{0.000004}

h = 0.000972 0.000004 h = \frac {0.000972}{0.000004}

h = 243 h= 243

So the length is 243 243

Azizul Islam
Dec 25, 2013

(4xπx0.09^3)/3=πx0.002^2xh

h=243m

Budi Utomo
Dec 25, 2013

V_sphere = V_wire ---> 4/3.phi.(180/2)^3 = phi.(4/2)^2.h ---> 4/3 . 729000/3 = 4 .h ----> 729000/3 [mm]= h ----> h = 243000/1000 [m] = 243 m. Answer : 243 . HAPPY CHRISTMAS DAY

Raj Magesh
Dec 25, 2013

The volumes of the sphere and the wire have to be equal, since the same material is used for both. The volume of a sphere of radius r r is 4 3 π r 3 \dfrac{4}{3}\pi r^{3} while the volume of a wire (which is in fact a very thin cylinder) is given by π r 2 l \pi r^{2}{l} , where r r is the radius of the wire and l l is its length.

Converting all given lengths to centimeters (for convenience):

V s p h e r e = 4 3 π ( 18 12 ) 3 = 972 π V_{sphere} = \dfrac{4}{3}\pi \left(\dfrac{18}{12}\right)^{3} = 972\pi

V c y l i n d e r = π ( 0.4 2 ) 2 l = 0.04 π l V_{cylinder} = \pi \left(\dfrac{0.4}{2}\right)^{2}l = 0.04\pi l

0.04 π l = 972 π \Rightarrow 0.04\pi l = 972 \pi

l = 24300 c m = 243 m \Rightarrow l = 24300 cm = \boxed{243 m}

Tan Tao
Dec 25, 2013

Volume of Sphere= 4/3 (pi)(r^3)=4/3(pi)(0.09)^3

Length of Wire=(4/3(pi)(0.09)^3) / ((pi)(0.002)^2)=243m

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