Mechanics Question and answers for complex exams.

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Mechanics solutions


Mechanics 1 (Vaal University of Technology)




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MECHANICS1 DEVELOPMENT TUTORIALS
TUTORIAL 5
1. A mass of 120 kg is suspended from a cord attached to two light inelastic ropes
which form angles of 30° and 45° with the horizontal. Calculate the tension in
each rope.
ANS: - The construction of the sketch has to be done before.




With base line A-A: ∑ F = 0
T1 sin 75° = 11772 sin 45°
T1 = 861.8 N
With base line B-B: ∑ F = 0
T2 sin 75° =11772 sin 60°
T2 = 10, 55 kN
2. A mass of 80 kg is suspended from a cord attached to two light inelastic ropes
with lengths of 3 m and 4 m respectively and their remaining ends are fixed 5 m
apart to the same horizontal beam. Calculate the tension in each rope.
ANS: - The construction of the sketch has to be done
before.




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C:\WINDOWS\hinhem.scr
Calculate the inside angles using cosine rule.
a2 = b2 + c2 – 2bcCos A
52 =32 + 42 – 2(3) (4) Cos A
A = 90°
Use sine rule to find other angles.
(Sin 90°)/5 = (sin B)/3
B = 36,87°
Use sine rule to find other angles.
(Sin 36,87)/3 = (sin C)/4
C = 53,13°
With a base line C-C: ∑ F = 0




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