A \(50-\mathrm{kg}\) ice skater moves across the ice at a constant speed of \(2.0 \mathrm{~m} / \mathrm{s}\). She is caught by her \(70-\mathrm{kg}\) partner, and then the pair continues to glide together. He is at rest when he catches her, and immediately afterward they both coast.

(a) What is their velocity just after the catch?

(b) A skater follows the girl at a constant speed of \(1.0 \mathrm{~m} / \mathrm{s}\). What is the girl's change in momentum in the reference frame of the skater?