Question

69 The resultant of two forces 3N and 4N making
an angel 90° with each other is
(a) 1 N
(b) 3N
(C) 5N
(d) 10 N​

Answer 1

Answer :

Magnitude of vector A = 3N

Magnitude of vector B = 4N

Angle between force vectors = 90°

We have to find resultant of both force vectors$.$

★ By triangle law or parallelogram law of vector addition, the magnitude of resultant R at two vectors A and B inclined to each other at angle θ, is given by

• R² = A² + B² + 2AB cosθ

By substituting the given values, we get

➠ R² = A² + B² + 2AB cosθ

➠ R² = 3² + 4² + 2(3)(4) cos90°

➠ R² = 9 + 16 + 24(0)

➠ R² = 25

➠ R = √25

➠ R = 5N

∴ (C) is the correct answer.