A bullet of mass m1 = 0.020 kg is fired with initial speed v1 into a block of mass m2 = 0.500 kg that is initially at rest. The bullet becomes embedded in the block and the pair slide along to the right a distance d= 0.35 m over a rough surface with u k = 0.25. the spring (with k = 450 N/m) is compressed by a distance of x = 0.075 m. work backwards and determine the initial velocity of the bullet.