Case A: A baseball pitched at 40 m/s collides with a catcher's mitt and is brought to a stop. The catcher holds the mitt with a relaxed arm and retracts backwards 30 cm as the ball strikes the mitt.
Case B: An identical baseball pitched at 40 m/s collides with a catcher's mitt and is brought to a stop. The catcher holds the mitt rather rigidly and retracts backwards very little as the ball strikes the mitt.

Which variable is different for these two cases?
(possible answers DELTA V, TIME and MASS