NCHMCT JEE 2015 Question Paper with solutions for online practice

Height of the 50 coins = 50 × 1 = 50 mm
r = 2 cm = 2 × 10 mm = 20 mm
$\mathit{\pi }{\mathit{r}}^2\mathit{H}$ = ${\mathit{\pi }}^2\mathit{R}\mathit{h}$
[Where h = length of wire]
⇒ 20 × 20 × 50 = ${\mathit{R}}^2$ × h
⇒ 20 × 20 × 50 = 1 × 1 × h
⇒ h = 20000 mm = 20 m
Hence, the length of the wire will be 20 m.