The radius of a wire is decreased to one-third. If volume remains the same, the length will become 3 times       (b)  6 times          (c)  9 times    (d)  27 times

Explanation

correct option is (c)9 times
`r_1=3x`
`r_2=x`
now `v_1=v_2`
`pir_1^2h_1=pir_2^2h_2`
putting the value of
`r_1` and `r_2`
`9h_1=h_2`