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A force of 5 units acts on a particle in the direction to the east...

Mathematics
JAMB 1978

A force of 5 units acts on a particle in the direction to the east and another force of 4 units acts on the particle in the direction north-east. The resultants of the two forces is

  • A. \(\sqrt{3}\) units
  • B. 3 units
  • C. \(\sqrt{41 + 20 \sqrt{2}}\) units
  • D. \(\sqrt{41 - 20 \sqrt{2}}\) units
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Correct Answer: Option C
Explanation

Force to the east = 5 units and angle to the east = 0º

force to the Northeast = 4 units and angle to northeast = 45º

Resolve these forces into x and y components

FORCES x - component y - component
5 5cos0 = 5 5sin 0 = 0
4 4cos45 = 4 x \(\frac{\sqrt2}{2}\) 4sin45 = \(\frac{\sqrt2}{2}\)
Total force  5 + 2\(\sqrt{2}\) 0 + 2\(\sqrt{2}\)

Resultant force = \(\sqrt{(F_x)^2 + (F_y)^2}\)

                         = \(\sqrt{ (5 + 2\sqrt{2})^2 + (2\sqrt{2})^2}\)

                        =  \(\sqrt{(25 + 20\sqrt{2} + 8) + 8}\)

                        =  \(\sqrt{33 + 20\sqrt{2} + 8}\) = \(\sqrt{41 + 20\sqrt{2}}\)


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