SUVAT Sign 실수 That Flip Your 답

Constant-가속도 equations only 일 if you pick one positive direction and stick to it. These traps show where signs usually go wrong.

v = u + at · s = ut + ½at² · v² = u² + 2as — Pick one positive axis for the whole problem

함정 1: Treating every slowdown as “a is negative” without a defined axis

틀림: Car slows from 20 m/s to 10 m/s → student writes a = −5 without saying which way is positive.

맞음: If forward is positive and the car slows while moving forward, a is negative. State the axis first.

수정: Negative 가속도 means 속도 is becoming less positive — not always “going backward.”

틀림: Walk 4 m forward and 1 m back → put s = 5 m into SUVAT.

맞음: 변위 is net change: s = +3 m if forward is positive. 거리 traveled is 5 m.

수정: SUVAT uses 변위 s, not total path length.

틀림: u = +12, a = −3, s = +16 → computing as if everything were positive magnitudes only.

맞음: Keep signed values: v² = (12)² + 2(−3)(16) = 144 − 96 = 48 → |v| = √48.

수정: Square roots give ±v; the sign of v comes from the physical direction you chose.

틀림: Taking up as positive for u but down as positive for g in the same line.

맞음: If up is positive, g ≈ −9.8 m/s². If down is positive, g ≈ +9.8 m/s². One choice only.

수정: 적으세요 “up positive” or “down positive” at the top of the 일ing.

틀림: Known u, v, t — but using s = ut + ½at² without finding a first (or picking the equation that omits a).

맞음: 사용하세요 s = ½(u + v)t when a is unknown, or find a = (v − u)/t first.

수정: List knowns, then pick the equation that does not need the missing symbol.

선택 one positive direction, write it down, and keep every u, v, a, and s consistent with that choice.

No. It means 속도 is decreasing along your positive axis. The 물체 can still be moving forward while slowing down.

No. 변위 is net position change (signed). 거리 is path length (≥ 0).