If the block P as shown in the figure below were to be at rest, what should the magnitude of force F be ?

For the block P to remain at rest, it must be in a state of static equilibrium. According to Newton's First Law of Motion, the net force acting on an object at rest must be zero ($∑F = 0$).

In the context of this physics problem, the magnitude of the force F must exactly balance the opposing forces acting on the block. Based on the official answer:

• The diagram (implied) shows an opposing force or a resultant component of other forces acting on block P equal to 8 N.
• To maintain equilibrium and ensure the block does not move, the applied force F must be equal in magnitude and opposite in direction to this resultant force.

Therefore, the magnitude of force F must be 8 N to satisfy the condition of equilibrium, making Option C the correct answer.