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Ch 11: Kinematics. AP Physics B Summer Course 2012 2012 年 AP 物理 B 暑假班. M Sittig. Describing motion. Scalars. Vectors. Displacement Velocity Acceleration Jerk…. Distance Speed …. Not commonly used. Practice Problem.
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Ch 11: Kinematics AP Physics B Summer Course 20122012年AP物理B暑假班 M Sittig
Describing motion Scalars Vectors Displacement Velocity Acceleration Jerk… • Distance • Speed • … Not commonly used.
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?
What is the difference between… Velocity Instantaneous velocity Acceleration • Speed • Average velocity • Velocity
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.
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!
Fundamental kinematics equations Number of stars = how many exponents each equation has.
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.
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.
Example Problem • What is the watermelon’s velocity when it hits the ground?
Practice Problem downward • What is the watermelon’s velocity when it hits the ground?
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.
Practice Problem • 5S pg 121 #4
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.
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.
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.
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?