Question

If we have two vectors of magnitude 4 and 3 respectively and angle between them is 120°, what is magnitude of resultant? ​

Answer 1

Answer:

Let the two vectors be P and Q and their resultant vector be R.

Let the angle between P and Q be θ.

Given: ∣P∣=3, ∣Q∣=4 and ∣R∣=5 units

Magnitude of resultant vector ∣R∣

2

=∣P∣

2

+∣Q∣

2

+2∣P∣∣Q∣cosθ

∴ 5

2

=3

2

+4

2

+2(3)(4)cosθ

We get cosθ=0

⟹θ=90

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