Question

A 0.79-kg ball is placed on top of a 2.5-kg book which is at the top of a table. What is the magnitude of the force exerted by the table to the two objects?

Answer 1

The magnitude of the force exerted by the table to the two objects is equal to the sum of their individual weights:

$$F = P_1+P_2$$

By definition, the weight of a non-moving body is:

$$P = mg$$

where $m$ is the mass of the body ($m_1 = 0.75kg$ for the first and $m_2 = 2.5kg$ for the second book) and $g = 9.8m/s^2$ is the gravitational acceleration. Thus, obtain:

$$F = g(m_1+m_2)\\ F = 9.8\cdot (0.75+2.5) \approx 18.4N$$

Answer. 18.4 N.