Question

Alicia draws a diagram to represent two forces, F1 and F2, acting on a body. The angle between the directions of the forces is 50° as shown in the diagram. Alicia notices that she can use the Law of Cosines to find the magnitude of the resultant force R in the diagram. What is the value of R?

Answer 1

Refer to the diagram shown below.

When the two forces F₁ and F₂ are added vectorially, the resultant force is R.
The angle x = 180° - 50° = 130°.

From the Law of Cosines, obtain
R² = F₁² + F₂² - 2F₁F₂ cos(130°)
Note that 2 cos(130°) = -1.2856.

Answer:
R = √(F₁²+ F₂² + 1.2856 F₁F₂ )

Answer 2

C. 70.7 is my best guess.