Diana L.

asked • 12/02/12

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?

Please help me do this problem..I am having problems with my homework?

2 Answers By Expert Tutors

By:

Roman C. answered • 12/02/12

Masters of Education Graduate with Mathematics Expertise

Robert J. answered • 12/02/12

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:
http://pad1.whstatic.com/images/thumb/a/a3/Find-the-Angle-Between-Two-Vectors-Step-1.jpg/550px-Find-the-Angle-Between-Two-Vectors-Step-1.jpg

nose-to-tail:
http://www.onlinemathlearning.com/image-files/vector-addition4.gif

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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.

Hope your great day.

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

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