1. Identify the system

Consider the block + cylinder together as one system.

Their total mass is $M = 5 + 25 = 30\ \text{kg}$

They move downward with acceleration $a = 0.1\ \text{m s}^{-2}$

2. Forces acting on the system

On the combined system, the external forces are:

• Weight downward: $Mg$
• Normal reaction of the floor on the system upward: $N$

Since the system accelerates downward, apply Newton's second law taking downward as positive: $Mg - N = Ma$

3. Substitute values

Using $g = 9.8\ \text{m s}^{-2}$, $30 \times 9.8 - N = 30 \times 0.1$ $294 - N = 3$ $N = 291\ \text{N}$

4. Action force on the floor

The floor exerts an upward force $N = 291\ \text{N}$ on the system. By Newton's third law, the action force of the system on the floor has the same magnitude and opposite direction.

Hence, the action force on the floor is $\boxed{291\ \text{N}}$

5. Check options

• A: $297\,\text{N}$ ❌
• B: $291\,\text{N}$ ✅
• C: $196\,\text{N}$ ❌
• D: $294\,\text{N}$ ❌

Therefore, the correct option is B.