Here it is given vertical post is 2.4 m high ,length of jib is 3.9 m long and tie is 2.1 m long
weight acting is 2.5 kN
since the line of action of all forces acts on a coincident point
so we can apply lami's theorem in it
and we can say that
"\\frac{W}{sin \\beta}=\\frac{J}{sin \\theta}=\\frac{T}{sin \\alpha}"
from above triangle we can find value of all sines
"sin \\beta=\\frac{2.4}{3.9}=0.615,sin \\theta=1,sin\\alpha=\\frac{2.1}{3.9}"
Now we take one pair at time for finding values
so ,
"\\frac{W}{sin \\beta}=\\frac{J}{sin \\theta}"
"\\frac{2.5}{0.615}=\\frac{J}{1}"
J=4.065 kN (compressive load) this is the force on jib
"\\frac{J}{sin \\theta}=\\frac{T}{sin \\alpha}"
"\\frac{4.065}{1}=\\frac{T}{0.538}"
T=2.18697 kN (Tension) this is the force on tie
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