Given that Force 1 = 70 pounds and Force 2 = 120 pounds , find the angle between the forces if the magnitude of the resultant force is 90 pounds . Round answer to the nearest

degree.

1 answer

70^2 + 120^2 + 2*70*120 cosθ = 90^2

cosθ = -2/3
θ = 131.8°

This makes sense, since if the two forces were separated by an acute angle, the resultant would be greater than either of them.

Think of the parallelogram involved.