A block $1$ rests on a horizontal surface and is connected by a light string over a frictionless pulley to a hanging block $2$. If block $2$ is heavier and tends to pull block $1$ to the right, in which direction does the static friction force act on block $1$?

• A. There is no static friction force acting on block $1$
• B. Upward, perpendicular to the surface
• C. To the left, opposing the motion that would occur if friction were absent
• D. To the right, in the same direction as the tension in the string

Answer: (C)

Verified step by step guidance

1. Identify the forces acting on block 1: the tension in the string pulling it to the right, the normal force upward, the gravitational force downward, and the static friction force opposing motion.
2. Understand that static friction acts to prevent relative motion between the block and the surface, so it will oppose the direction in which block 1 would slide if friction were absent.
3. Since block 2 is heavier and pulls block 1 to the right, block 1 tends to move rightward, so static friction must act to the left to oppose this motion.
4. Recognize that static friction acts parallel to the surface, so it cannot act upward or downward; it must act horizontally to the left in this scenario.
5. Conclude that the static friction force on block 1 acts to the left, opposing the motion that would occur if friction were absent.