1.

Theresultantof two forces, one double the other in magnitude, is perpendicular to the smaller of the twoforces. The angle between the two forces is(a) 60°(b) 120°(c) 150°(d) 90°6. A weightless ladder 30 s o

Answer»

Let two forces F₁ and F₂ are givenA/C to question, |F₁| = 2|F₂|Resultant of two forces F₁ and F₂ are given by R = F₁ + F₂

A/C to question, R is perpendicular upon smaller force.Here smaller force is F₂.So, R.F₂ = 0⇒(F₁ + F₂).F₂ = 0⇒F₁.F₂ + F₂² = 0 ⇒|F₁||F₂|cosФ + |F₂|² = 0 Now, put |F₁| = 2|F₂| ⇒2|F₂|.|F₂|cosФ + |F₂|² = 0⇒2cosФ + 1 = 0 ⇒cosФ = -1/2 = cos120°

Hence, angle between two forces is 120°



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