In a spring gun having spring constant 100N m ^ - 1 a small ball B...

$\dfrac{1}{2}k{x}^{2} = \dfrac{1}{2}m{v}^{2}$
$K{x}^{2} = m{v}^{2}$
$v = x\sqrt{\dfrac{k}{m}} = 0 . 05\sqrt{\dfrac{100}{0 . 1}} = 0 . 05 \times 10\sqrt{10}$
$v = 0 . 5\sqrt{10}$
From $h = \dfrac{1}{2}g{t}^{2}$
$t = \sqrt{\dfrac{2h}{g}} = \sqrt{\dfrac{2 \times 2}{10}} = \dfrac{2}{\sqrt{10}}$
$∴ d = vt = 0 . 5\sqrt{10} \times \dfrac{2}{\sqrt{10}} = 1m$