Three forces in equilibrium: if two are equal and at 120°, third force is:
A. Equal to each, at 120° to both
B. Difference of two
C. Sum of two
D. Zero
Answer: Option A
Solution (By JKSSB Mock Tests)
Vector equilibrium: three equal forces at 120° form closed triangle. Third force equals magnitude of others, oriented 120° from each. Memory aid: 'Equilibrium: vector sum = 0; symmetric forces ⇒ symmetric angles'. Statics concept frequently tested in competitive exams.
Explanation:
Work done to charge a capacitor is stored as electrostatic potential energy in the electric field between plates: U = ½QV = ½CV² = Q²/(2C). This energy can be recovered when capacitor discharges. Heat (A) is dissipated in resistance during charging, but ideal capacitor stores energy electrostatically. Memory aid: 'Capacitor energy = ½CV², stored in electric field'. This electrostatics concept is frequently tested in competitive exams. Always distinguish ideal capacitor (no resistance) from real circuits where some energy is lost as heat during charging.
Explanation:
For perpendicular forces: R = √(F₁² + F₂²) = √(9 + 16) = √25 = 5 N. Pythagorean theorem applies for vector addition at 90°. Memory aid: '3-4-5 triangle for perpendicular forces'. Basic vector addition problem testing magnitude calculation, common in mechanics sections of competitive exams.
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