9. A bullet of mass 15 g and travelling at a speed of \( 600 \mathrm{~m} / \mathrm{s} \) strikes a block of mass 3 kg which is suspended by a string of length 4 m . The bullet goes through the block in a very short time and the center of mass of the block is found to rise a vertical distance of 10 cm as shown in the figure below. What was the speed of the bullet just after it emerged from the block?