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4. Vectors A and B have equal magnitudes of 5. If A + B = 6j, then find the angle between A and B.​

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Final answer:

To find the angle between two vectors A and B with magnitudes of 5 and a resultant of 6j, we used vector algebra and trigonometry, concluding that the angle is approximately 73.74 degrees.

Step-by-step explanation:

If we have two vectors A and B with equal magnitudes of 5 and they sum up to give a resultant vector which is 6j, the angle between vectors A and B can be calculated using vector algebra and trigonometry. Since the resultant is solely in the j-direction (which is the vertical direction in the xy-plane) and has a magnitude of 6, it implies that the horizontal components of vectors A and B must cancel each other out.

Let θ be the angle between vector A and vector B. We can use the cosine rule for vectors, which states that when two vectors of equal magnitude “A” add to a resultant vector “R” making angle θ with each other, their resultant R equals A∙sqrt(2∙2∙cos(θ)). Our resultant vector has a magnitude of 6, and each of the original vectors has a magnitude of 5. Therefore, we can write:

6 = 5∙sqrt(2∙2∙cos(θ))

Squaring both sides, we get:

36 = 50∙2∙50∙cos(θ)


=> cos(θ) = 7/25

Using a calculator, we find that:

θ ≈ cos-1(7/25)

θ ≈ 73.74°

Therefore, the angle between vectors A and B is approximately 73.74 degrees.

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