Question

A meter rule is hung by two light strip tied at the 15cm, and 75 cm mark respectively to a
ceiling. If the weight of the ruler is 2N. (i) calculate the tension in the two string.

Answer 1

Draw the diagram:

According to equilibrium of forces:

$$T_A+T_B-W=0,\\\space\\ T_A+T_B=W=2\text N.$$

The total tension in the two strings is 2N.

Find the torque around point A:

$$\frac{15}{2}·2·(15/100)-\frac{85}{2}·2·(85/100)+60·T_B=0,\\\space\\ T_B=1.17\text N.\\ T_A=2-T_B=0.83\text N.$$