Final answer:
The angle between two forces cannot be determined without context, but the principles of Newton's second law, friction, and mechanics of inclined planes must be used to study the forces and their relation to each other.
Step-by-step explanation:
The angle between two forces acting on a block depends on the direction of the individual forces. However, the scenarios given in the question don't provide enough information to directly determine the angle θ. Instead, each example provides a context in which you must apply the principles of Newton's second law and concepts of friction, inclined plane mechanics, and tension in strings to ascertain the forces at play and how they relate to one another. For instance, if you're asked to calculate forces on an inclined plane with a specific friction coefficient, you'd need to calculate the normal force, then use the coefficient of friction to find the frictional force before finally using Newton's second law to determine the net force and subsequently the acceleration.