High School

A girl exerts a horizontal force of 139 N on a box with a mass of 30.7 kg.

(a) If the box doesn't move, what's the magnitude of the static friction force (in N)?

Answer :

The magnitude of the static friction force is 139 N, which counters the applied horizontal force to keep the box stationary. This ensures a state of equilibrium with no movement.

  1. Since the box is not moving, the static friction force must be equal in magnitude to the applied force but in the opposite direction to balance it out.
  2. This tells us that the magnitude of the static friction force f_s is 139 N.

To summarize, the magnitude of the static friction force is 139 N because it must counterbalance the applied horizontal force.

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