Physics

The power ball has now reached its highest point above the ground and starts to descend again. The motion

 

diagram representing the velocity vectors is the same as that after the initial release, as shown in the figure of Part

 

B. Indicate whether the velocity and acceleration of the ball at its highest point are positive (upward), negative, or

 

zero.

 

 

 

Use P, N, and Z for positive (upward), negative, and zero, respectively. Separate the letters for velocity and

 

 

 

 

acceleration with a comma.

 

 

 

 

Hint 1. Velocity as a continuous function of time

 

 

 

 

In Part D you found that the velocity of the ball is positive during the upward motion. Once the ball starts its

 

descent, its velocity is negative, as you found in Part B. Since velocity changes continuously in time, it has to

 

be zero at some point along the path of the ball.

 

 

 

Hint 2. Acceleration as a continuous function of time

 

 

 

 

In Part D, you found that the acceleration of the ball is negative and constant during the upward motion, as

 

well as once the ball has started its descent, which you found in Part B. Since acceleration is a continuous

 

function of time, it has to be negative at the highest point along the path as well.

 

 

 

2.- 2 . 0 Ã2 . 0

 

0 – 0 Ã0

 

 

 

 

P,N

 

 

 

11/10/2014 HW_Week2

 

http://session.masteringphysics.com/myct/assignmentPrintView?assignmentID=2992507 19/29

 

 

ANSWER:

 

 

 

Correct

 

 

 

 

These examples should show you that the velocity and acceleration can have opposite or similar signs or that

 

 

one of them can be zero while the other has either sign. Try hard to think carefully about them as distinct

 

 

 

physical quantities when working with kinematics.

 

 

Analyzing Position versus Time Graphs: Conceptual Question

 

 

Two cars travel on the parallel lanes of a twolane

 

road. The

 

cars’ motions are represented by the position versus time

 

graph shown in the figure. Answer the questions using the

 

times from the graph indicated by letters.

 

 

 

Part A

 

 

 

 

At which of the times do the two cars pass each other?

 

 

 

Hint 1. Two cars passing

 

 

 

 

Two objects can pass each other only if they have the same position at the same time.

 

ANSWER:

 

 

 

Z,N

 

 

 

11/10/2014 HW_Week2

 

http://session.masteringphysics.com/myct/assignmentPrintView?assignmentID=2992507 20/29

 

 

Correct

 

 

 

Part B

 

 

 

 

Are the two cars traveling in the same direction when they pass each other?

 

ANSWER:

 

 

 

Correct

 

 

 

Part C

 

 

 

 

At which of the lettered times, if any, does car #1 momentarily stop?

 

 

 

Hint 1. Determining velocity from a position versus time graph

 

 

 

 

The slope on a position versus time graph is the “rise” (change in position) over the “run” (change in time). In

 

physics, the ratio of change in position over change in time is defined as the velocity. Thus, the slope on a

 

position versus time graph is the velocity of the object being graphed.

 

ANSWER:

 

A

 

B

 

C

 

D

 

E

 

None

 

Cannot be determined

 

yes

 

no

 

A

 

B

 

C

 

D

 

E

 

none

 

cannot be determined

 

 

 

11/10/2014 HW_Week2

 

http://session.masteringphysics.com/myct/assignmentPrintView?assignmentID=2992507 21/29

 

 

Correct

 

 

 

Part D

 

 

 

 

At which of the lettered times, if any, does car #2 momentarily stop?

 

 

 

Hint 1. Determining velocity from a position versus time graph

 

 

 

 

The slope on a position versus time graph is the “rise” (change in position) over the “run” (change in time). In

 

physics, the ratio of change in position over change in time is defined as the velocity. Thus, the slope on a

 

position versus time graph is the velocity of the object being graphed.

 

ANSWER:

 

 

 

Correct

 

 

 

Part E

 

 

 

 

At which of the lettered times are the cars moving with nearly identical velocity?

 

 

 

Hint 1. Determining Velocity from a Position versus Time Graph

 

 

 

 

The slope on a position versus time graph is the “rise” (change in position) over the “run” (change in time). In

 

physics, the ratio of change in position over change in time is defined as the velocity. Thus, the slope on a

 

position versus time graph is the velocity of the object being graphed.

 

ANSWER:

 

A

 

B

 

C

 

D

 

E

 

none

 

cannot be determined

 

 

 

11/10/2014 HW_Week2

 

http://session.masteringphysics.com/myct/assignmentPrintView?assignmentID=2992507 22/29

 

 

Correct

 

 

 

 

Conceptual Question 2.05

 

 

Part A

 

 

 

 

Suppose that an object is moving with constant nonzero acceleration. Which of the following is an accurate

 

statement concerning its motion?

 

ANSWER:

 

 

 

Correct

 

 

 

 

Conceptual Question 2.09

 

 

Part A

 

 

 

 

The graph in the figure shows the position of an object as a function of time. The letters HL

 

represent particular

 

moments of time. At which moments shown (H, I, etc.) is the speed of the object

 

A

 

B

 

C

 

D

 

E

 

None

 

Cannot be determined

 

In equal times its speed changes by equal amounts.

 

In equal times its velocity changes by equal amounts.

 

A graph of its position as a function of time has a constant slope.

 

In equal times it moves equal distances.

 

A graph of its velocity as a function of time is a horizontal line.

 

 

 

11/10/2014 HW_Week2

 

http://session.masteringphysics.com/myct/assignmentPrintView?assignmentID=2992507 23/29

 

 

(a) the greatest?

 

ANSWER:

 

 

 

Correct

 

 

 

Part B

 

 

 

 

(b) the smallest?

 

ANSWER:

 

 

 

Correct

 

 

 

 

Conceptual Question 2.04

 

 

Part A

 

 

 

 

H

 

I

 

J

 

K

 

L

 

H

 

I

 

J

 

K

 

L

 

 

 

11/10/2014 HW_Week2

 

http://session.masteringphysics.com/myct/assignmentPrintView?assignmentID=2992507 24/29

 

 

When can we be certain that the average velocity of an object is always equal to its instantaneous velocity?

 

ANSWER:

 

 

 

Correct

 

 

 

 

Conceptual Question 2.18

 

 

Part A

 

 

 

 

Two objects are thrown from the top of a tall building and experience no appreciable air resistance. One is thrown

 

up, and the other is thrown down, both with the same initial speed. What are their speeds when they hit the street?

 

ANSWER:

 

 

 

Correct

 

 

 

 

Conceptual Question 2.16

 

 

Part A

 

 

 

 

The figure represents the velocity of a particle as it travels along the xaxis.

 

At what value (or values) of is the

 

 

 

 

instantaneous acceleration equal to zero?

 

always

 

only when the acceleration is constant

 

never

 

only when the acceleration is changing at a constant rate

 

only when the velocity is constant

 

The one thrown down is traveling faster.

 

The one thrown up is traveling faster.

 

They are traveling at the same speed.

 

 

 

11/10/2014 HW_Week2

 

http://session.masteringphysics.com/myct/assignmentPrintView?assignmentID=2992507 25/29

 

 

ANSWER:

 

 

 

Correct

 

 

 

 

Problem 2.27

 

 

Part A

 

 

 

 

A package is dropped from a helicopter moving upward at 15 m/s. If it takes 8 s before the package strikes the

 

ground, how high above the ground was the package when it was released if air resistance is negligible?

 

ANSWER:

 

 

 

Correct

 

 

 

 

Problem 2.10

 

 

Part A

 

 

 

 

= 1 s

 

= 0.5 s and = 2 s

 

= 0

 

 

 

 

190 m

 

114 m

 

152 m

 

228 m

 

 

 

11/10/2014 HW_Week2

 

http://session.masteringphysics.com/myct/assignmentPrintView?assignmentID=2992507 26/29

 

 

The position of an object as a function of time is given by x = bt2 ct,

 

where = 2.0 m/s2 and = 6.7 m/s, and and

 

are in SI units. What is the instantaneous velocity of the object when = 2.3?

 

 

 

 

ANSWER:

 

 

 

Correct

 

 

 

 

Conceptual Question 2.02

 

 

Part A

 

 

 

 

If the graph of the position as a function of time for an object is a horizontal line, that object cannot be accelerating.

 

ANSWER:

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