AP Physics B Summer Course 2012 2012 年 AP 物理 B 暑假班

1. Ch 11: Kinematics AP Physics B Summer Course 20122012年AP物理B暑假班 M Sittig

2. Describing motion Scalars Vectors Displacement Velocity Acceleration Jerk… • Distance • Speed • … Not commonly used.

3. Practice Problem • Mr. Ant, standing in an elevator, moves up 40 m with the elevator. He then gets out of the elevator and walks along a straight hallway for 3 minutes at a speed 10 meters/minute. What is the magnitude of Mr. Ant’s net displacement?

4. What is the difference between… Velocity Instantaneous velocity Acceleration • Speed • Average velocity • Velocity

5. Practice Problem • Which of the following cars has a westward acceleration? • A car traveling eastward and speeding up. A car traveling westward and slowing down. A car traveling westward at constant speed. A car traveling eastward and slowing down.

6. Solving kinematics problems • Remember the fundamental kinematics equations. • Know which quantities each equation has, and doesn’thave. • Fundamental kinematics equations only apply for constant velocity. • Use the table of variables – unique to 5S, and very useful!

7. Fundamental kinematics variables

8. Fundamental kinematics equations Number of stars = how many exponents each equation has.

9. Physics Problem Solving

10. Kinematics Problem Solving • Step 1: Write out all five variables in a table. Fill in known values, put “?” next to unknown values. • Step 2: If 3 or more known values, continue to Step 3. Otherwise, check your work. • Step 3: Choose the equation that has all of the knowns and the desired unknown. Solve. • Step 4: Put the correct units on your answer.

11. Example Problem

12. Practice Problem

13. Freefall • Acceleration due to gravity is a = -10 m/s2when gravity is the only force on the object. • The horizontal motion of an object will NOT affect its fall – time to fall depends only on the vertical position/motion.

14. Example Problem • What is the watermelon’s velocity when it hits the ground?

15. Practice Problem downward • What is the watermelon’s velocity when it hits the ground?

16. Projectile Motion • Break the velocity into vector components. • We can work with the vector components separately because they are independent of each other. • • The y-component of velocity, vy, equals v(sin θ). • • The x-component of velocity, vx, equals v(cos θ). • • Horizontal velocity is constant. • • Vertical acceleration is g, directed downward. • • Time is the variable that is the same for x and y.

17. Example Problem

18. Practice Problem v

19. Practice Problem • 5S pg 121 #4

20. Motion Graphs • The slope of a position–time graph at any point is the velocity of the object at that point in time. • The slope of a velocity–time graph at any point is the acceleration of the object at that point in time. • The area under a velocity–time graph between two times is the displacement of the object during that time interval.

21. Describe the motion

22. Describe the motion

23. Practice Problem • The following data shows the positions of a car at times 0, 2, 4, 6, 8 and 10 s. Match the list of positions with the graph to which it corresponds. • 0.0, 32.5, 65.0, 97.5, 130.0, 167.5 m. • 0.0, 8.0, 32.0, 72.0, 120.0, 168.0 m. • 0.0, 55.0, 120.0, 168.0, 168.0, 168.0 m.

24. Practice Problem • The graph shows the speed of a car traveling in a straight line as a function of time. • The value of Vc is 3.80 m/s and the value of Vd is 5.30 m/s. Calculate the distance traveled by the car from a time of 1.20 to 5.20 seconds.

25. Super Challenge Problem • A student walks into an elevator at rest on the bottom floor of a building with 4 stories. The elevator then accelerates upward with an unknown constant acceleration a during a time interval Δt1 = t, moves at a constant velocity for Δt2 = 6t, and then decelerates at the same magnitude a for time interval Δt3 = t. If the elevator rises a total of h meters, what is the magnitude of the acceleration a given time t and height h?