Paper 2 · November 2025 · couples; resultant of coplanar forces; gravitational potential; geostationary orbit

Two forces of 12 N and 10 N act at the same point on an object, with an angle of 60 degrees between their lines of action. Calculate the magnitude of their resultant force.

Model answer

19.1 N

Also accepted: 19.1, 19 N, 19.08 N

Explanation

Using the parallelogram (cosine) rule for two forces with angle

\theta

between them,

R^2 = F_1^2 + F_2^2 + 2F_1F_2\cos\theta

. Here

R^2 = 12^2 + 10^2 + 2(12)(10)\cos 60 = 144 + 100 + 120 = 364

, so

R = \sqrt{364} = 19.1

N. The plus sign is used because 60 degrees is the angle between the forces themselves, not the angle of the triangle of forces.

Derived from ZIMSEC Physics Paper 2, November 2025, Q1

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