Question

roberto is applying force to the left on a desk. the desk is not moving because the applied force is balanced by static friction. what must be true about the force of static friction?

a) it must be as strong as robertos applied force and to the left.
b) it must be weaker than robertos applied force and to the left.
c) it must be stronger than robertos applied force but directed into the floor.
d) it must be as strong as robertos applied force but to the right.

Explanation:

When forces are balanced, the net force is zero. Static friction acts in the opposite direction to the applied force. Since Roberto's force is to the left, static friction must be to the right. And for the forces to balance (so that the desk doesn't move), the magnitudes of the applied force and the static - friction force must be equal.

Answer:

D. It must be as strong as Roberto’s applied force but to the right.