Bill s ball goes up and comes back down to Bill s level. At that point, it is

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1 ConcepTest 2.1 Up in the Air Alice and Bill are at the top of a cliff of height H.. Both throw a ball with initial speed v 0, Alice straight down and Bill straight up. The speeds of the balls when they hit the ground are v A and v B. If there is no air resistance, which is true? 1) v A < v B 2) v A = v B 3) v A > v B 4) impossible to tell Alice v 0 v v 0 Bill H v A v B

2 ConcepTest 2.1 Up in the Air Alice and Bill are at the top of a cliff of height H.. Both throw a ball with initial speed v 0, Alice straight down and Bill straight up. The speeds of the balls when they hit the ground are v A and v B. If there is no air resistance, which is true? 1) v A < v B 2) v A = v B 3) v A > v B 4) impossible to tell Bill s ball goes up and comes back down to Bill s level. At that point, it is moving downward with v 0, the same as Alice s ball. Thus, it will hit the ground with the same speed as Alice s ball. Alice v v 0 v A v 0 v B Bill H

3 ConcepTest 2.2 Graphing Velocity The graph shows position as a function of time for two trains running on parallel tracks. Which is true: 1) At time t B, both trains have the same velocity. 2) Both trains speed up all the time. 3) Both trains have the same velocity at some time before t B. 4) S h th h b th t i 4) Somewhere on the graph, both trains have the same acceleration.

4 ConcepTest 2.2 Graphing Velocity The graph shows position as a function of time for two trains running on parallel tracks. Which is true: 1) At time t B, both trains have the same velocity. 2) Both trains speed up all the time. 3) Both trains have the same velocity at some time before t B. 4) Somewhere on the graph, both trains have the same acceleration. To find velocity from a position-time graph, look at the slope of the lines. Both trains have the same velocity at the instant the slopes of the lines are parallel as indicated in the figure above.

5 ConcepTest 2.3 Acceleration Acar traveling along a horizontal, flat road starts from rest and experiences an acceleration, a = 8 * t, where t denotes time. Which of the following statement(s) is (are) correct? I. v f (t) =8*t 2 II. III. x f (t) =x 0 + 1/2 * (8*t) 2 v f (t) =4*t 2 IV. x f (t) = x 0 + 1/2 * (4*t) 2 1) Only I is correct. 2) Only II is correct. 3) Only III is correct. 4) Only I and II are correct. 5) Only III and IV are correct. 6) No answer choice is correct.

6 ConcepTest 2.3 Acceleration Acar traveling along a horizontal, flat road starts from rest and experiences an acceleration, a = 8 * t, where t denotes time. Which of the following statement(s) is (are) correct? I. v f (t) =8*t 2 II. III. x f (t) =x 0 + 1/2 * (8*t) 2 v f (t) =4*t 2 IV. x f (t) = x 0 + 1/2 * (4*t) 2 1) Only I is correct. 2) Only II is correct. 3) Only III is correct. 4) Only I and II are correct. 5) Only III and IV are correct. 6) No answer choice is correct.

7 ConcepTest 2.4 Ferris Wheel Consider a student riding on a Ferris wheel at a carnival. If the Ferris wheel rotates counterclockwise at a constant rate, which of the vectors A, B, C,.. shown best describes the average acceleration of the student as she moves from point P to point S.

8 ConcepTest 2.4 Ferris Wheel Consider a student riding on a Ferris wheel at a carnival. If the Ferris wheel rotates counterclockwise at a constant rate, which of the vectors A, B, C,.. shown best describes the average acceleration of the student as she moves from point P to point S. v i v f -v i f For average acceleration, we need to consider the initial and final velocities. a avg ~ v f -v i

9 ConcepTest 3.1 Firing Balls A cart is being pulled along a horizontal track by an external source (a weight hanging over the table edge) and is accelerating. It fires a ball straight up out of the cannon as it moves. After it is fired, what happens to the ball? 1) it depends upon how much the track is tilted 2) it falls behind the cart 3) it falls in front of the cart 4) it falls right back into the cart 5) it remains at rest

10 ConcepTest 3.1 Firing Balls A cart is being pulled along a horizontal track by an external source (a weight hanging over the table edge) and is accelerating. It fires a ball straight up out of the cannon as it moves. After it is fired, what happens to the ball? 1) it depends upon how much the track is tilted 2) it falls behind the cart 3) it falls in front of the cart 4) it falls right back into the cart 5) it remains at rest The acceleration (component parallel to the table) of the cart is completely unrelated to the ball. Once the ball is fired it does not have any horizontal acceleration at all so it will lag behind the accelerating cart.

11 ConcepTest 3.2 Projectile A projectile is launched from the ground at an angle of 30 o. At what point in its trajectory does this projectile have the least speed? 1) just after it is launched 2) at the highest point in its flight 3) just before it hits the ground 4) halfway between the ground and the highest point 5) speed is always constant

12 ConcepTest 3.2 Projectile A projectile is launched from 1) just after it is launched the ground at an angle of 2) at the highest point in its flight 30 o. At what point in its 3) just before it hits the ground trajectory does this projectile have the least speed? 4) halfway between the ground and the highest point 5) speed is always constant The speed is smallest at the highest point of its flight path because the y- component of the velocity is zero.

13 Which of the ConcepTest 3.3 Punts 3 punts has the longest hang time? ) all have the same hang time h

14 Which of the ConcepTest 3.3 Punts 3 punts has the longest hang time? ) all have the same hang time h The time in the air is determined by the vertical motion! Since all of the punts reach the same height, they all stay in the air for the same time.

Honors Physics Acceleration and Projectile Review Guide

Honors Physics Acceleration and Projectile Review Guide Major Concepts 1 D Motion on the horizontal 1 D motion on the vertical Relationship between velocity and acceleration Difference between constant