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Ch. 7 - Applications of Trigonometry and Vectors
Lial - Trigonometry 12th Edition
Lial12th EditionTrigonometryISBN: 9780136552161, 9780135440780, 9780136881117, 9780135440827, 9780135924891Non è quello che usi tu?Cambia libro di testo
Capitolo 8, Problema 36

A force of 28.7 lb makes an angle of 42° 10′ with a second force. The resultant of the two forces makes an angle of 32° 40′ with the first force. Find the magnitudes of the second force and of the resultant.


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1
Convert all given angles from degrees and minutes to decimal degrees for easier calculation. For example, 42° 10′ becomes \(42 + \frac{10}{60}\) degrees, and similarly for 32° 40′.
Let the magnitude of the second force be \(F_2\) and the magnitude of the resultant force be \(R\). The first force \(F_1\) is given as 28.7 lb.
Use the Law of Cosines to relate the magnitudes of the forces and the angle between them. The angle between the two forces is \$42° 10′$, so write the equation: \(R^2 = F_1^2 + F_2^2 + 2 F_1 F_2 \cos(42° 10′)\)
Use the Law of Sines to relate the angles and sides in the triangle formed by the two forces and their resultant. The resultant makes an angle of \$32° 40′$ with the first force, so write: \(\frac{F_2}{\sin(32° 40′)} = \frac{R}{\sin(42° 10′ + 32° 40′)}\)
Solve the system of two equations from steps 3 and 4 simultaneously to find the unknown magnitudes \(F_2\) and \(R\).

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