Question

5.1.5 quiz: describing forces
which statement best describes the forces shown in this picture?
a. all four forces are acting on the student.
b. the force of friction and the gravitational force are balanced.
c. the normal force and the gravitational force are balanced.
d. the force of friction is less than the applied force

Explanation:

• Option A: The applied force (\(F_{app}\)) is acting on the wall, not the student. So, not all four forces are acting on the student.
• Option B: The force of friction (\(F_{fric}\)) acts horizontally, and the gravitational force (\(F_{grav}\)) acts vertically. Forces in perpendicular directions cannot balance each other.
• Option C: The normal force (\(F_{norm}\)) acts vertically upward, and the gravitational force (\(F_{grav}\)) acts vertically downward. For an object at rest (assuming the student is in equilibrium vertically), these two forces balance each other (\(F_{norm}=F_{grav}\) when there is no vertical acceleration).
• Option D: There is no information to suggest the student is accelerating horizontally. If the student is at rest horizontally (no motion), the force of friction would be equal to the applied force (if there was an applied force on the student in the horizontal direction. But \(F_{app}\) is on the wall).

Answer:

C. The normal force and the gravitational force are balanced.