A prismatic bar ABC is subjected to an axial load of 25kN; the reactions RA and RC will be
A
RA=−10kN and RC=−15kN
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B
RA=10kN and RC=−35kN
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C
RA=−15kN and RC=−10kN
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D
RA=15kN and RC=−40kN
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Solution
The correct option is CRA=−15kN and RC=−10kN The free body diagram of the given figure is shown below.
∴ Equilibrium condition for the bar is given by RA+RB=25 ... (i)
Compatibility condition for the bar is given by ΔAB+ΔBC=0 .. (ii)
But ΔAB=RA×2LAE (tensile) ΔBC=RB×3LAE (compressive)
Substituting values of ΔAB and ΔBC in (ii), we get RA×2LAE−RB×3LAE=0 [from (i)] ⇒RA×2L−(25−RA)×3L=0 ⇒2RA−75+3RA=0 ⇒RA=15kN
ALso, RB=25−15=10kN
Since the forces left to right directions are taken as positive, therefore, the reactions which are acting from right to left are negative.