AP Physics 1 Questions on Work Done by Non-Conservative Forces

📚 Quick Study Guide

• 🔑 Work Done by Conservative Forces: Independent of the path taken (e.g., gravity, spring force). The work done around a closed path is zero.
• 📏 Work Done by Non-Conservative Forces: Depends on the path taken (e.g., friction, air resistance, applied force). The work done around a closed path is not zero.
• 🔥 Non-Conservative Work and Energy: $W_{nc} = \Delta E = E_f - E_i$, where $W_{nc}$ is the work done by non-conservative forces, and $E$ is the total mechanical energy (kinetic + potential).
• 📉 Friction: Always opposes motion and dissipates energy as heat. The work done by friction is always negative: $W_f = -f d$, where $f$ is the frictional force and $d$ is the distance traveled.
• 💨 Air Resistance: A type of friction that depends on the speed of the object. The work done by air resistance also dissipates energy.
• 💪 Applied Force: If an external force is applied that changes the total energy of the system, it's a non-conservative force.

🧪 Practice Quiz

1. A box is pushed across a rough horizontal surface at a constant speed. Which of the following statements is true about the work done on the box?
   1. The work done by friction is zero.
   2. The work done by the applied force is zero.
   3. The net work done on the box is zero.
   4. The net work done on the box is positive.
2. A block slides down a rough inclined plane. Which of the following forces is non-conservative?
   1. The normal force.
   2. The gravitational force.
   3. The frictional force.
   4. The component of gravity parallel to the plane.
3. A roller coaster car is moving along a track. At which point is the work done by friction the greatest?
   1. At the highest point of the track.
   2. At the lowest point of the track.
   3. When the car is moving at a constant speed.
   4. The work done by friction is the same at all points.
4. A person pushes a box up a ramp at constant speed. What forces are doing work on the box?
   1. Gravity only.
   2. Applied force only.
   3. Gravity and friction only.
   4. Gravity, friction, and applied force.
5. An object is moved in a closed loop on a horizontal surface with friction. The work done by friction:
   1. Is zero.
   2. Is positive.
   3. Is negative.
   4. Depends on the path.
6. A ball is thrown upwards. Which of the following statements is true considering air resistance?
   1. Mechanical energy is conserved.
   2. Air resistance does positive work.
   3. Air resistance does negative work.
   4. Kinetic energy is always increasing.
7. A crate is pulled across a floor by a rope. The tension in the rope does work on the crate. If the crate moves at a constant velocity, the work done by friction is:
   1. Equal to the work done by tension.
   2. Greater than the work done by tension.
   3. Less than the work done by tension.
   4. Zero.