Question

A uniform pole 7m long and weighing 10kg is supported by a boy 2m from one end and a man 3m from the other end.At what point must a 20kg weight be attached so that the man would support thrice as much weight as the boy?

Answer 1

Sum of moments relative to the boy

$$\sum M=-3\times N\times 2+M\times g\times x+m\times g=0$$

Sum of moments relative to the man

$$\sum M=-N\times 2+m\times g+M\times g\times (2-x)$$

Solve the resulting system of equations

$$x=4 meter$$

Point must a 20kg weight be attached so that the man would support thrice as much weight as the boy is located 4 metres from the boy and 2 metres from the man