For each of the following, put \"A\" if it is always true, \"S\" ifit is sometimes true, or \"N\" if it is never true.
(a) The net force on an object is zero if its speed remainsconstant.
(b) Normal force cannot do work on any system.
(c) If mechanical energy is not conserved, friction is thereason.
(d) A person riding a ferris wheel will feel heaviest at thebottom.
(e) If a moving object changes direction, a net force must acton it.
(f) The terminal velocity of a 25 kg object is higher than thatof a 10 kg object.
