High school physics quiz: Static and kinetic friction questions.

📚 Quick Study Guide

• 🍎 Friction: A force that opposes motion between surfaces in contact.
• 🧱 Static Friction ($f_s$): The force that prevents an object from starting to move. $f_s \le \mu_s N$, where $\mu_s$ is the coefficient of static friction and $N$ is the normal force.
• 🏃 Kinetic Friction ($f_k$): The force that opposes the motion of a moving object. $f_k = \mu_k N$, where $\mu_k$ is the coefficient of kinetic friction and $N$ is the normal force.
• 📈 Coefficients of Friction: $\mu_s$ (static) is usually greater than $\mu_k$ (kinetic) for the same pair of surfaces.
• 📐 Normal Force (N): The force exerted by a surface that is supporting the weight of an object. On a horizontal surface, it is equal to the object's weight: $N = mg$.
• 💡 Key Difference: Static friction acts on objects at rest, while kinetic friction acts on objects in motion.
• 📝 Important Formulas:
  • Static friction: $f_s \le \mu_s N$
  • Kinetic Friction: $f_k = \mu_k N$

🧪 Practice Quiz

1. A box is at rest on a horizontal surface. A horizontal force is applied to the box, but it does not move. What type of friction is acting on the box?
   1. Static friction
   2. Kinetic friction
   3. Rolling friction
   4. Fluid friction
2. A book is sliding across a table. What force opposes the motion of the book?
   1. Static friction
   2. Kinetic friction
   3. Normal force
   4. Applied force
3. The coefficient of static friction between a rubber tire and dry asphalt is 0.90, while the coefficient of kinetic friction is 0.70. What does this indicate?
   1. It's easier to start sliding the tire than to keep it sliding.
   2. It's harder to start sliding the tire than to keep it sliding.
   3. Static and kinetic friction are equal.
   4. The normal force is negligible.
4. A 10 kg block is at rest on a horizontal surface. The coefficient of static friction between the block and the surface is 0.4. What is the maximum static friction force that can act on the block before it starts to move? (Assume g = 9.8 m/s²)
   1. 39.2 N
   2. 98 N
   3. 4 N
   4. 0 N
5. A 5 kg box is sliding across a floor with a coefficient of kinetic friction of 0.3. What is the force of kinetic friction acting on the box? (Assume g = 9.8 m/s²)
   1. 14.7 N
   2. 49 N
   3. 1.5 N
   4. 0 N
6. Which of the following factors does NOT affect the force of friction between two surfaces?
   1. The type of materials in contact
   2. The normal force between the surfaces
   3. The area of contact between the surfaces
   4. The coefficient of friction
7. A car is driving on a flat, horizontal road. What type of friction is primarily responsible for allowing the car to accelerate forward?
   1. Kinetic friction
   2. Static friction
   3. Rolling friction
   4. Fluid friction