Final answer:
The magnitude of force F required to move the block up the ramp at constant velocity is 15N, which is the sum of the gravitational force component parallel to the ramp (10N) and the force of friction (5N).
Step-by-step explanation:
To determine the magnitude of force F required to move the block up the ramp at a constant velocity, we need to consider the forces acting parallel to the ramp's surface. Since the block is moving at a constant velocity, the net force in the direction of the block's motion must be zero. That means the force applied (F) must exactly counterbalance the force of gravity pulling the block down the ramp and the force of friction.
The component of the gravitational force pulling the block down the ramp is the weight of the block times the sine of the angle of the incline (20N * sin(30 degrees)). The force of gravity component parallel to the ramp is 10N. The force of friction Ff, given as 5N, also opposes the motion. Therefore, the total force F needed to pull the block up the ramp with constant velocity is the sum of these two forces: 10N + 5N = 15N. So the answer is (b) 15N.