**Force Applied by the Inclined Plane on the Block**

To determine the force applied by the inclined plane on the block, we need to consider the forces acting on the block. These forces include the gravitational force, the normal force, and the frictional force.

**1. Gravitational Force:**
The gravitational force is the force exerted on the block due to its mass. It can be calculated using the equation: F_gravity = m * g, where m is the mass of the block and g is the acceleration due to gravity (approximately 9.8 m/s²).

In this case, the mass of the block is given as 5 kg. Therefore, the gravitational force acting on the block is F_gravity = 5 kg * 9.8 m/s² = 49 N.

**2. Normal Force:**
The normal force is the force exerted by a surface to support the weight of an object resting on it. It acts perpendicular to the surface. In this case, the normal force is equal to the component of the gravitational force acting perpendicular to the inclined surface.

Since the block is at rest on the inclined surface, the normal force must balance the gravitational force acting perpendicular to the surface. Therefore, the normal force is equal in magnitude but opposite in direction to the gravitational force, which is 49 N.

**3. Frictional Force:**
The frictional force is the force that opposes the motion or tendency of motion of an object sliding along a surface. It acts parallel to the surface and can be calculated using the equation: F_friction = μ * N, where μ is the coefficient of friction and N is the normal force.

The coefficient of friction depends on the roughness of the surface. Since the inclined surface is described as rough, we can assume a non-zero coefficient of friction. Let's assume the coefficient of friction is 0.2.

Therefore, the frictional force can be calculated as: F_friction = 0.2 * 49 N = 9.8 N.

**4. Force Applied by the Inclined Plane:**
Finally, the force applied by the inclined plane on the block can be determined by considering the forces acting along the inclined surface. The force applied by the inclined plane is equal in magnitude but opposite in direction to the frictional force.

Therefore, the force applied by the inclined plane on the block is 9.8 N, directed in the opposite direction to the motion of the block.

This question may be tricky if your basics are not clear.. you may think the question as " what is the normal reaction?" .. the normal reaction will be mg cos theta = 50 � 1/2 Newton.. but it is not the only force acting on the block by the plane.. friction is also a force that is acting upon the block by the plane.. and as the block is resting, the friction force = mg sin theta = 50 � √3/4 Newton ..