(1) When the jetpack is rapidly sprayed downward, the gas is subjected to downward force, and at the same time, the gas generates upward reaction force on the backpack, indicating that the forces between objects are mutual.

(2) Because the rocket man keeps flying at a constant speed, regardless of air resistance, the rocket man is subjected to gravity and upward thrust, and the two forces are a pair of balanced forces, so the direction of gas ejected from the backpack should be vertical downward.

So, the answer is: mutual; Vertical downward.