Answer:
7.85 N
Step-by-step explanation:
The measuring stick is uniform so we can safely assume that all of its mass is concentrated at the center.
The center is at 7/2 i.e 3.5 meter mark.
Given that it is balanced, the sum of clockwise force is equal to the sum of clockwise force according to the principle of moments. The 1 meter mark is the pivotal point.
Torque = Force * distance(perpendicular to the force);
It is balanced so:
Torque due to 2 kg rock = torque due to weight of the measuring stick;
2 * 9.81 * 1 = x *9.81 * (3.5-1); x is the mass of the measuring stick;
x= 0.8 kilograms
Weight = 0.8 *9.81 =7.85 N