A bullet of mass $10\,g$ moving horizontally with a velocity of $400 \, ms^{-1}$ strikes a wooden block of mass $2 \,kg$ which is suspended by a light inextensible string of length $5\, m$. As a result, the centre of gravity of the block is found to rise a vertical distance of $10\,cm$. The speed of the bullet after it emerges out horizontally from the block will be -