الشغل vs القدرة أخطاء (Joules vs Watts)

الشغل is طاقة transferred (joules). القدرة is how fast that happens (watts). الامتحانات punish mixing them.

W = F d · P = W/t · P = F v — 1 W = 1 J/s · convert minutes → seconds

فخ 1: Calling قدرة “شغل” because both use W

خطأ: P = 50 W described as “50 joules of شغل.”

صحيح: 50 W means 50 joules every second. الشغل would need a time: W = P t.

التصحيح: تحقق the unit: J → شغل/طاقة; W (watt) → قدرة.

خطأ: 600 J في 2 minutes → P = 600/2 = 300 W.

صحيح: t = 120 s → P = 600/120 = 5 W.

التصحيح: Always convert minutes × 60 قبل القسمة for watts.

خطأ: Any F and any v multiplied, even when قوة is perpendicular to motion.

صحيح: استخدم the component of قوة along the سرعة متجهة: P = F v cosθ (or F_parallel × v).

التصحيح: P = Fv is the special case when قوة and سرعة متجهة are parallel.

خطأ: A lifting problem answered with P = VI because “قدرة is VI.”

صحيح: Mechanical: P = W/t or P = Fv. Electric circuits: P = VI (or I²R, V²/R).

التصحيح: Match the صيغة to the context — motors can involve both, but the given data tells you which.

خطأ: Two lifts of 100 J must both be “the same قدرة.”

صحيح: Same شغل في less time means more قدرة: 100 J في 2 s → 50 W; في 10 s → 10 W.

التصحيح: القدرة always needs a time (or a سرعة with قوة).

Joules are شغل; watts are joules per second. حوّل time to seconds, and only use P = Fv when قوة lines up with سرعة متجهة.

الشغل (J) is طاقة transferred. القدرة (W) is the rate of that transfer: P = W/t.

حول 746 W for mechanical horseقدرة بالمترost school conversions.