A-LevelMathematicsMechanics9709/42 · Feb/Mar 2017 · Q26 Marks
A particle P of mass 1.6 kg is suspended in equilibrium by two light inextensible strings attached to points A and B. The strings make angles of 20° and 40° respectively with the horizontal (see diagram). [Figure 2]
- Find the tensions in the two strings.[6]
This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.
Mark scheme
Marking points from the official mark scheme (Feb/Mar 2017). The mark or mark type is shown in brackets.
- [M1] Resolve forces horizontally and/or vertically
- [A1] Correct vertical equation: TA Sin 20 + TB Sin 40 = 16
- [A1] Correct horizontal equation: TA COS 20 = TB COS 40
- [M1] Attempt to solve for TA and/or TB
- [A1] TA = 14.2N TA = 14.1528...
- [A1] TB = 17.4N TB = 17.3610...
- [M1] Attempt to use Lami's Theorem
- [A1] (16 / sin 120) = (TA / sin 130)
- [A1] (16 / sin 120) = (TB / sin 110)
- [M1] Attempt to solve for TA and/or TB
- [A1] TA = 14.2 N
- [A1] TB = 17.4 N
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