In a spring gun having spring constant $100 \mathrm {~N} \mathrm {~m} ^ { - 1 }$ a small ball $B$ of mass 100 g is put in its barrel (as shown in figure) by compressing the spring through 0.05 m . There should be a box placed at a distance $d$ on the ground so that the ball falls in it. If the ball leaves the gun horizontally at a height of 2 m above the ground. The value of $d$ is $\underline{\hspace{1cm}}$ m.
$$\left( g = 10 \mathrm {~m} \mathrm {~s} ^ { - 2 } \right)$$