A bullet of mass 10g and unknown speed is shot horizontally into a block of mass 990g, initially at rest on a horizontal frictionless surface. The bullet embeds itself in the block, and the combined objects slide along the surface until they encounter a horizontal spring of spring constant 400N/m. The block, with the bullet in it, comes to momentarily rest when it has compressed the spring by 10 cm. Find the initial speed of the bullet