Question

A copper rod of diameter 1 cm and length 8 cm is drawn into a wire of length 18 cm of uniform thickness. Find the thickness of the wire.

Answer 1

Diameter of copper wire =1 cm
Radius  cm
Height of copper rod =Length of copper rod =8 cm
Volume of rod 

Let the radius of wire be ‘r’ cm
Height of the wire =18 m =0.18 cm
Volume of cylinder wire = Volume of cylindrical rod


⇒ r2
⇒ r  cm
⇒ r = 1/3 mm
∴ Diameter of cross section = (1/3) × 2 mm
= 0.67 mm

Answer 2

Cylindrical rod:
Diameter (D) = 1 cm
⇒ Radius (R) =
Height of rod (H) = length of rod = 8 cm
∴ Volume of rod = πR2H

Cylindrical rod is drawn into a cylindrical wire of length (h) 18 m (= 1800 cm)
∴ Volume of cylindrical rod = volume of cylindrical wire
Let r be the radius of cross-section of the wire.

So, the diameter of the cross-section(approx) 
Hence, thickness of the wire = 0.67 mm 


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