Question Collision Energy Changes Practice Test

Yuki sets up a line of standing dominoes on a desk. She gently tips the first domino so it falls into the next one. Before each collision, one domino is moving and the next is still. After each hit, the next domino begins to fall. What question about motion and energy could this collision help answer?

Keisha lifts and releases one ball in a Newton’s cradle so it swings into the still balls and clicks. Looking at this setup, which question asks about energy changes in this collision?