Question

The radius of a wire is decreased to one-third. if volume remains the same, length will increase by

Answer 1

volume = 2*pi*r^2*l
therefore
2*pi*r^2*l = 2*pi*(r/3)^2*l(changed)
=.r^2*l = (r^2/9)*l(changed)
so, l(changed) = 9*l
therefore, length will become 9 times.