Question

Difficulty: MediumScalars and Vectors

A particle is subjected to two mutually perpendicular horizontal forces of magnitudes 15 N15\text{ N} acting due East and 20 N20\text{ N} acting due South. What is the magnitude of the resultant force acting on the particle?

  1. 25 N25\text{ N}Answer
  2. B
    35 N35\text{ N}
  3. C
    5 N5\text{ N}
  4. D
    13.2 N13.2\text{ N}

Answer

The magnitude of the resultant force acting on the particle is 25 N25\text{ N}.
Because the two forces act at right angles (9090^\circ) relative to each other, vector addition requires applying the Pythagorean theorem. Squaring both component magnitudes (152=22515^2 = 225 and 202=40020^2 = 400), summing them to obtain 625625, and taking the square root gives the resultant magnitude of 25 N25\text{ N}.

Step-by-Step Solution

1
Identify the force components and their geometric orientation
The East force component Fx=15 NF_x = 15\text{ N} and the South force component Fy=20 NF_y = 20\text{ N} meet at an angle of 9090^\circ.
Perpendicular vectors form the adjacent and opposite sides of a right-angled vector triangle.
2
Apply the Pythagorean theorem to find the hypotenuse representing the resultant force
R=Fx2+Fy2=152+202=225+400=625=25 NR = \sqrt{F_x^2 + F_y^2} = \sqrt{15^2 + 20^2} = \sqrt{225 + 400} = \sqrt{625} = 25\text{ N}.
The resultant of two orthogonal vector quantities equals the square root of the sum of their individual squares.

Key Concept

Vector Addition of Perpendicular Forces
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