A 2 kg block sits on a horizontal, frictionless surface and is attached to a massless horizontal spring with spring constant 2000 N/m. A 15 g bullet is fired into the block, in the face opposite the spring, and sticks into the block. After the bullet hits the block, they both begin to move in simple harmonic motion. What is the bullet's velocity before the collision, if the amplitude of the resulting oscillations is 8 cm?