A-LevelMathematicsMechanics9709/43 · Oct/Nov 2019 · Q36 Marks

Three coplanar forces of magnitudes 50 N, 60 N and 100 N act at a point. The resultant of the forces has magnitude R N. The directions of these forces are shown in the diagram. Find the values of R and α.

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Mark scheme

Marking points from the official mark scheme (Oct/Nov 2019). The mark or mark type is shown in brackets.

[M1] Resolving horizontally or vertically
[A1] 50cos20 + 60 - 100sin30 (=56.984...)
[A1] 100cos30 - 50sin20 (= 69.501...)
[M1] Method to find either R or α (R = √(56.984...² + 69.501...²) or α = tan⁻¹(56.984... / 69.501...))
[A1] R=89.9 (89.876...)
[A1] α=39.3 (39.348...)

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Topic: Mechanics, A-Level Mathematics (syllabus 9709). Structured question, 6 marks.
Source: A-Level Mathematics, Oct/Nov 2019 Paper 4 Variant 3, question 3.

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