Here’s the explanation for each question based on the content of the image:

Question 3:

Between the values for $\mu_s$ and $\mu_k$, which is larger? Why?

Answer:
The value of $\mu_s$ (the coefficient of static friction) is larger than $\mu_k$ (the coefficient of kinetic friction).

Why?

• Static friction ($\mu_s$) is the force that prevents an object from starting to move when a force is applied. It requires more force to overcome this initial resistance because the object and the surface have "locked" together at a microscopic level.
• Kinetic friction ($\mu_k$) acts when the object is already moving. Once the object is in motion, there is less resistance because the microscopic "locking" between the surfaces has been broken.

Thus, $\mu_s > \mu_k$ because it is harder to start an object moving than to keep it moving.

Question 4:

For an object sliding across a surface at constant speed, is the force of friction greater than, less than, or equal to the applied force?

Answer:
The force of friction is equal to the applied force.

Why?

• When an object is moving at a constant speed, the net force acting on it is zero (according to Newton's First Law of Motion). This means that all the forces acting on the object balance each other.
• The applied force is exactly balanced by the force of kinetic friction. If the applied force were greater, the object would accelerate; if it were less, the object would slow down and stop.

Question 5:

What is the net force of an object sliding across a horizontal surface at constant speed? Why?

Answer:
The net force is zero.

Why?

• According to Newton's First Law of Motion, if an object is moving at a constant speed, there is no acceleration. This happens when the forces acting on the object are balanced.
• On a horizontal surface, the applied force is balanced by the kinetic friction force. Since these forces cancel each other out, the net force (which is the sum of all forces acting on the object) is zero.

Questions for Deeper Understanding:

1. What is the formula for calculating the force of friction, and how does it involve $\mu$?
2. Why does kinetic friction not depend on the speed of the object?
3. How does the normal force affect the frictional force between two surfaces?
4. Can static friction ever exceed the applied force? Why or why not?
5. How does friction vary if the surface is inclined rather than horizontal?

Tip:

When analyzing friction problems, always identify whether the object is stationary or in motion. This helps determine whether to use $\mu_s$ or $\mu_k$.