The problem in the image describes a system involving three blocks, $A$, $B$, and $C$, of masses $m_A$, $m_B$, and $m_C$, respectively. Here's the key information extracted:

• Blocks $A$ and $B$ are on a horizontal surface with negligible friction.
• Block $A$ is attached to the table.
• Block $C$, of mass $m_C$, is suspended by a string that passes over a pulley and is connected to Block $B$.
• The entire system is at rest.

The question asks: Which of the following gives the magnitude of the force exerted by Block A on Block B?

Solution Approach:

1. Force Analysis for Block B: Block $B$ is being pulled horizontally by the tension in the string, which is also connected to Block $C$. Since the system is in equilibrium (at rest), the tension force $T$ in the string will be equal to the weight of Block $C$: $T = m_C g$ where $g$ is the acceleration due to gravity.

2. Force exerted by Block A on Block B: Since Block $A$ is attached to the table, it must exert a reaction force to keep Block $B$ stationary. This force is equal to the tension $T$, which is the same as $m_C g$.

Final Answer:

The force exerted by Block $A$ on Block $B$ is the tension in the string, which is: $\boxed{m_C g}$

Let me know if you'd like to explore the problem further or have any questions!

Here are 5 related questions to deepen your understanding:

1. How would the force change if the surface had friction?
2. What happens if the mass of Block C increases?
3. How would the system behave if Block B were lighter than Block C?
4. What role does the pulley play in this system?
5. Can you calculate the tension if the blocks were accelerating?

Tip: In a static system like this, always start by analyzing the forces in equilibrium!