 Diana L.

# Two forces of 55N and 85N act on an object simultaneously and the resultant force is 125N. What is the measurement of the angle between the two forces?

## 2 Answers By Expert Tutors

By: Tutor
4.6 (13)

Certified High School AP Calculus and Physics Teacher Daniel O.

Shouldn't the angle between them be: 180 - 125.09? 125 degrees is the angle between them if you placed the force vectors nose-to-tail, but that isn't what I'd consider to be the angle between two vectors; it should be the angle between them when they're tail-to-tail.

Diana, see these diagrams if you're confused by what I mean:

tail-to-tail:

nose-to-tail:

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12/03/12

Sung taee L.

Dear Robert.J.

Your calculation is quite right. But should we have to reconsider the angle between the two vectors ? I think it should be a suplement of the calculated angle.

Sung

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12/03/12 Robert J.

Yes, you are correct. I used head to tail picture to get angle between the two sides, but not between the two forces.

The angle between the two vectors should be the supplement angle of what I calculated.

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12/03/12 John M.

tutor
Too complicated. If the 85N force is acting on the object, the parallel force from the 55N force is ArcCosine(40/55) = 43.34 degrees. Or, work it with the 55N directly on the object and it needs 70N to equal 125N, so the angle is 55.94 degrees.
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12/16/19 Liz Z.

tutor
I also got 55.9 degrees. We need the angle adjacent to the 125.09 measurement.
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13d

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