It's very small so no harm in doin it. Just involves restitution equation which you do in collisions anyway. Such a small thing that I don't think it's worth leaving out of your practice. On the day if it comes up you can probably work it out without studying anyway because it's just a combo of collisions and projectiles.
Projectiles is't predicted to come up this year because it came up a lot in recent years, they'll probably swap it out for a pair production question instead, but we only need to do 5 questions this year so you should be fine anyway debby