Question

A uniform rod of length 1m and mass 20 kg Is supported horizontally on 2 knife edges at the ends. Two masses of 6 kg and 10 kg are suspended at 0.3m and 0.7m from one end of the rod. Find the reactions on the knife edges.

Answer 1

Sum of the upward forces = sum of the downward forces.

R₁ + R₂ = P + Q + W = 6 + 10 + 20

= 36 kg wt.

Taking moments about A

P × AB + W × AC + Q × AD = R₂ × AE

6 × 0.3 + 20 × 0.5 + 10 × 0.7 = R₂ × 1

1.8 + 10 + 7 = R₂ = 18.8kgwt

R₁ + 18.8 = 36

R₁ = 17.2 kg wt.