2019 AP Physics 1 Solutions Free Response #1
TLDRIn this video, Alan from Bottle Stem Coach discusses the 2019 AP Physics free response questions. He analyzes a scenario involving two blocks on a frictionless surface, one of which is pushed by a mechanical plunger. He explains the acceleration and deceleration phases, the effect of friction, and how the system's motion and angular momentum change throughout the process.
Takeaways
- 📚 Alan from Bottle Stem Coach is discussing the 2019 AP Physics free response questions without solutions, which will be released later.
- 🔍 The problem involves identical blocks on a frictionless surface, except between points C and D where there is friction.
- 🔧 Block 1 is pushed by a mechanical plunger from point A to B, after which it continues moving towards block 2.
- 💥 After collision at point E, blocks 1 and 2 stick together and move as a system across the surface.
- 📈 The task is to sketch the speed of the center of mass of the two-block system from time T_a until block 1 passes point F.
- 🚀 The system experiences constant acceleration from A to C due to the constant force of the plunger.
- 🛑 At point C, the net force decreases due to friction, causing a decrease in acceleration.
- 🔄 From D to E, the system continues with the same velocity as there is no external force acting on it after the collision.
- 🌀 The second part of the problem involves a uniform solid sphere pushed by the plunger from A to B, with the force directed towards the center of mass.
- 🔄 The sphere's angular momentum changes only between points C and D due to the torque caused by friction.
- 🏁 After point D, the sphere continues rolling at a constant speed, and its angular momentum does not change.
Q & A
What is the scenario described in the 2019 AP Physics free response question?
-The scenario involves identical blocks on a frictionless surface, except for a rough region between points C and D. A block is pushed with a constant horizontal force from point A to B by a mechanical plunger. Upon reaching point B, the block loses contact with the plunger and collides with another block at point C, causing them to stick together and move as a system across the surface.
What is the initial force applied to the block system?
-The initial force applied to the block system is a constant horizontal force from the mechanical plunger, denoted as FP.
Why does the block system's acceleration change from point A to C?
-The block system's acceleration changes from point A to C because it enters a rough region between points C and D, where friction acts against the motion, reducing the net force and thus the acceleration.
What happens to the block system's acceleration after it loses contact with the plunger at point B?
-After losing contact with the plunger at point B, the net force on the block system becomes zero, leading to zero acceleration and a deceleration phase due to the frictional force.
How does the block system's motion change from point D to E?
-From point D to E, the block system continues moving at the same velocity as it did before the collision, as there is no external force acting on the system.
What is the role of the plunger's force in the system's motion from point A to B?
-The plunger's force is responsible for the initial acceleration of the block system from point A to B, providing a constant horizontal force that propels the system forward.
Why does the block system's speed profile change between points C and D?
-The speed profile changes between points C and D because the frictional force acts against the motion, causing the system to decelerate and resulting in a shallower slope in the speed-time graph.
What is the significance of the frictional force in the system's motion?
-The frictional force is significant as it opposes the motion of the block system, causing it to decelerate and eventually stop accelerating, affecting the system's speed and acceleration.
What is the scenario involving the uniform solid sphere in the script?
-A uniform solid sphere is placed at point A and pushed by a plunger from point A to B with a constant horizontal force. After losing contact with the plunger at point B, the sphere continues moving across the surface towards point E.
When does the sphere's angular momentum change in the described scenario?
-The sphere's angular momentum changes between points C and D, where the frictional force acts as a torque, causing the sphere to begin rotating.
Why does the sphere's angular momentum not change after point D?
-After point D, the sphere continues rolling at a constant speed, and since there is no external torque acting on it, its angular momentum remains constant.
Outlines
🚀 Physics Problem: Two Blocks and a Plunger
In this paragraph, Alan from Bottle Stem Coach discusses the 2019 AP Physics free response questions, specifically focusing on a scenario involving two identical blocks on a frictionless surface, except for a rough region between points C and D. The problem describes a mechanical plunger pushing block one from point A to B, after which it loses contact and continues moving towards block two. Upon collision, the blocks stick together and move as a system. The task is to sketch the speed of the center of mass of the two-block system as a function of time from the start until the block passes point F. Alan explains the dynamics of the system, including constant acceleration from A to C, deceleration due to friction from C to D, and constant velocity from D to E after the collision. He also clarifies that the net force on the system is zero from B to C and from D to E, as there is no external force acting on the system.
🌀 Angular Momentum and Torque in a Sphere's Motion
The second paragraph continues the discussion on the 2019 AP Physics free response questions, focusing on a uniform solid sphere pushed by a plunger from point A to B. The sphere loses contact with the plunger at point B and moves across the surface towards point E. Alan explains that the angular momentum about the center of mass changes only when a torque is applied, which happens due to the frictional force between C and D. He emphasizes that the plunger force is directed towards the center of mass and does not cause a torque, but the frictional force does, leading to rotation. The angular momentum remains constant after the sphere exits the frictional area, as there is no further torque applied. Alan concludes the explanation by highlighting that the only interval where the torque and thus the angular momentum changes is between points C and D.
Mindmap
Keywords
💡Free Response Questions
💡Plungers
💡Constant Horizontal Force
💡Frictionless Surface
💡Rough Surface
💡Constant Acceleration
💡Net Force
💡Kinetic Friction
💡Angular Momentum
💡Torque
💡Uniform Solid Sphere
Highlights
Alan from Bottle Stem Coach discusses the 2019 AP Physics free response questions.
The solutions for these questions are not yet available but will be released in a few months.
The question involves identical blocks on a frictionless surface, except between points C and D.
Block one is pushed from point A to B by a mechanical plunger.
Upon reaching point B, block one loses contact with the plunger and continues moving towards block 2.
Block 1 collides and sticks to block 2 at point E, after which they move together as a system.
The task is to sketch the speed of the center of mass of the two-block system as a function of time.
The net force on the system from A to C is the force from the plunger (FP).
From C to D, the net force is FP minus the force of friction due to the rough surface.
The plunger force is constant, but the net force decreases due to friction, leading to a shallower slope in acceleration.
Between D and E, the net force is zero as the blocks move together without external forces.
The plunger returns to its original position, and a uniform solid sphere is placed at point A.
The sphere is pushed from A to B by a constant horizontal force directed toward its center of mass.
The sphere loses contact with the plunger at point B and continues moving towards point E.
The angular momentum about its center mass changes only between points C and D due to friction.
The force of friction causes a torque, leading to a change in angular momentum.
After point D, the sphere continues rolling at a constant speed, and its angular momentum does not change.
The only time torque is applied is between C and D, affecting the sphere's angular momentum.
Transcripts
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