A 12-inch ruler rests on your right index finger at the 6-inch mark. Required:
a. What forces are present?
b. Write the first and second equations of equilibrium fully and show that both conditions are satisfied.

Explanation:

Let the right index finger be the pivot, the balanced ruler is shown in the diagram attached to this answer.

a. The forces present are:

i. The weight of the ruler, W, which acts upwards at the point of pivot.

ii. The reaction, R, of the right index finger on the ruler which acts upwards.

b. According to the principle of equilibrium, the total forces acting upwards must be equal to the total forces acting downwards.

So that,

R = W ................. 1

ii. The sum of clockwise moment must be equal to the sum of anticlockwise moment.

Since the ruler is balanced at the mid-point (6 inch), then;

R x 0 = w x 0 = 0 ............... 2

This implies that no moment is experienced by the ruler balanced on the right index finger. Therefore, the ruler is said to be in a state of equilibrium.

if the person is shown to have +90n, then ans is -10n.

if the person is shown to have -90n, then ans is +10n.

i think it would be 5