A 9.00 g bullet, moving horizontally with an initial speed v, embeds itself in a 1.20 kg pendulum bob that is initially at rest. The length of the pendulum is L = 0.700 m. After the collision, the pendulum swings to one side and comes to rest when it has gained a vertical height of 13.0 cm.
a) Find the initial speed of the bullet.
b) How long does it take for the bullet-bob system to come to rest for the first time?