Answer:
Explanation:
Given
Mass of alice [tex]M_a=50 kg[/tex]
Mass of bob [tex]M_b=70 kg[/tex]
Mass of beam [tex]M=20 kg[/tex]
Suppose fulcrum is at distance of d from bob thus From diagram
Equating torque i.e. torque of Bob,Alice and beam must cancel out each other to be balanced
[tex]500\times (8-d)+20\times (4-d)=70\times d[/tex]
[tex]400-50d+80-2d=70d[/tex]
[tex]480=140d[/tex]
[tex]d=\frac{480}{140}[/tex]
[tex]d=3.43 m[/tex]
