A bullet of mass 0.1 kg is fired on a wooden block to pierce through it, but it stops after moving a distance of 50 cm into it. If the velocity of the bullet before hitting the wood is $10 \mathrm {~m} \mathrm {~s} ^ { - 1 }$ and, it slows down with uniform deceleration, then the magnitude of effective retarding force on the bullet is $x \mathrm {~N}$. The value of $x$ to the nearest integer is