To determine the force of friction when Polly is pushing a box to the right with a force of 30 N and the box does not move, let's analyze the situation step-by-step.
1. Identify Given Forces:
- Polly pushes the box to the right with a force of 30 N.
- The gravitational force acting downwards on the box is 8 N.
- The normal force acting upwards on the box is 8 N.
Since Polly is pushing the box to the right with a horizontal force, we can ignore the vertical forces (gravitational and normal forces) in our calculation of the friction force because they are balanced and don't affect the horizontal motion directly.
2. Static Friction Concept:
- Static friction is the force that resists the initiation of sliding motion between two surfaces in contact.
- The friction force will act in the opposite direction to Polly's push to prevent the box from moving if Polly's push is not strong enough to overcome it.
3. Force Balance:
- If Polly cannot move the box, it implies that the force of static friction is exactly equal in magnitude and opposite in direction to the force Polly is applying.
- Polly is applying a 30 N force to the right.
- Therefore, the friction force must be 30 N to the left to completely cancel out Polly's push.
4. Conclusion:
- Based on this analysis, the force of friction which opposes Polly's 30 N push and prevents the box from moving should also be 30 N in the opposite direction (to the left).
5. Result:
- The value that describes the force of friction is [tex]\( \leftarrow 30 \, \text{N} \)[/tex].
Hence, the correct value that could describe the force of friction if Polly could not move the box is [tex]\( \leftarrow 30 \, \text{N} \)[/tex].
