Answer:
b.The frictional force and force exerted by the spring scale on the block, because they are a Newton's third-law pair.
Step-by-step explanation:
Students connect a spring scale to a block on a rough horizontal surface. The students use the spring scale to measure the magnitude of the horizontal force needed to pull the block at a constant speed. Which of the following statements explains why two forces exerted between objects ar equal in magnitude?
a.A The gravitational and normal forces exerted on the block, because they are a Newton's third-law pair.
b.The frictional force and force exerted by the spring scale on the block, because they are a Newton's third-law pair.
c.The normal force and the frictional force exerted on the block, because objects always exert forces of equal magnitude on each other.
d.The frictional forces that the block and the surface exert on each other, because objects always exert forces of equal magnitude on each other.
solution \
the answer will be B
for a body to travel in a horizontal direction, it must be equal in direction to the frictional force which is in opposite direction to the force applied to move the block.
Also Newton's third law of motion must be obeyed , which states that action and reaction are equal and opposite