NIFT UG 2019 Question Paper with solutions

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Question : 16 of 150

Marks: +1, -0

A copper rod of

1 {cm}

diameter and

8 {cm}

length is drawn into a wire of uniform diameter and

18 {m}

length. The radius (in

{cm}

) of wire is

$\;{1}/{15}$
$\;{1}/{30}$
$\;{2}/{15}$
15

Solution:

Volume of copper used

=π r^{2} h

=π ×(\;{1}/{2})^{2} × 8=2 π {cm}^{3}

Now, it is made into another wire of height

18 {m}

.

∴ \;\;

Volume

=π r^{2}[(18 × 100) {cm}]

⇒ \;\; 2 π=π r^{2}(1800)

⇒ \;\; r^{2}=\;{2}/{1800}

⇒ \;\; r=\;{1}/{30}

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