A bullet of mass 2.5 g is fired horizontally into a wood block of mass 12 kg that is suspended from the ceiling by massless strings. The bullet becomes embedded in the block, and the block is observed to swing upward to a maximum height of 0.35 m from its initial position.
(a) Find the speed of the bullet just before it hit the block.
(b) Find the change in the kinetic energy of the system. Explain how microscopic energy is conserved in this process.