chapter 2 : motion in one dimension

Question 1

distance

Answer 1

magnitude of displacement, must be non-negative

Question 2

displacement

Answer 2

change in position

Question 3

does the displacement of an object depend on the location chosen for the origin of the coordinate system?

Answer 3

No, bcz displacement is the difference between two coordinates

• the position of an object does depend on the origin

Question 4

average speed

Answer 4

total distance traveled / time it takes to travel that distance

• cannot be negative

Question 5

average velocity

Answer 5

displacement / time it took to get there

• denoted by meters/second
• make sure to write the direction it goes in in the answer

Question 6

You drive to msp, stay a while, then drive home. The total trip takes 8 hours. What is average velocity and average speed?

Answer 6

average velocity = 0 m/s
(0 miles)/(8 hours) = 0

average speed = 54 mi/ hr
(217 + 217)/ (8 hours) = 54

Question 7

You drive for 30 minutes at 30 mi/hr and then for another 30 minutes at 50 mi/hr. What is your average speed for the whole trip?

Answer 7

( 15 miles + 25 miles) / ( 1 hour) = 40 mi/hr

Question 8

instantaneous velocity

Answer 8

average velocity over an infinitesimally short interval of time

Question 9

instantaneous speed

Answer 9

magnitude of instantaneous velocity, equals the absolute value of velocity

Question 10

average acceleration

Answer 10

when velocity is changing over an interval of time

(v2 - v1) / (t2 - t1 ) = acceleration

• denoted by m/s^2
• speeding up, slowing down, or change in direction

Question 11

Decelerating

Answer 11

the magnitude of its velocity is getting smaller

Question 12

A car accelerates 0 mph - 60 mph in 7.8 seconds. What is its average acceleration in m/s^2 ?

Answer 12

60 mph = 26.8 m/s
(26.8 m/s - 0 m/s) / ( 7.8 seconds) = 3.4 m/s^2

Question 13

You drive for 30 minutes at 30 mi/hr and then for another 30 minutes at 50
mi/hr. What is your average speed for the whole trip?

Answer 13

equal to 40 mi/hr

Question 14

Andrew throws an apple straight up into the air. After it leaves his hand, at what
point in its flight is the apple’s acceleration greatest?

Answer 14

the acceleration is constant everywhere

Question 15

A car slows down from 25 m/s to rest in a distance of 85 m. What was its
acceleration, assumed constant?

Answer 15

We are given the starting speed 𝑣𝑣0 (25 m/s), ending speed 𝑣𝑣 (rest), and
displacement ∆𝑥𝑥 (85 m), and we want to find acceleration.
Let’s use 𝑣2 = 𝑣0
2 + 2𝑎( 𝑥 − 𝑥0) and solve for 𝑎:

-3.7 m/s^2

Question 16

Jenny and Brett are on the roof of a building holding watermelons over the
edge. Jenny throws her watermelon upward, while Brett simply drops his. Just
after release, which watermelon has the greater acceleration? Ignore air
resistance.

Answer 16

Both have the same acceleration

Question 17

You drop a rock off a high bridge over a river. When
the rock has fallen four meters, you drop a second
rock. As the two rocks continue to fall, what
happens to the separation between them?

Answer 17

The separation increases as they fall

Question 18

A baseball is hit almost straight up into the air with a speed of about 20 m/s.
(a) How high does it go? (b) How long is it in the air?

Answer 18

a.) 20 meters
b.) 4 seconds

Question 19

The position of a rabbit along a straight tunnel as a
function of time is plotted in the graph to the right.
What is its average velocity (a) for the first 35 seconds
and (b) over the entire time interval? (c) When does
its instantaneous velocity first become negative?

Answer 19

a.) 0.57 m/s
b.) The final position is 𝑥𝑥 = 10 m, so ̅ 𝑣𝑣 = 10 m
50 s = 0.20 m/s
c.) Its instantaneous velocity is negative when the
slope is negative, which first occurs somewhere
around t = 38 seconds

Question 20

Suppose that an object travels from one point in space to another in a series of steps. Make a comparison between the displacement and the distance traveled.

Answer 20

The displacement is either less than or equal to the distance traveled.

Question 21

A new car manufacturer advertises that their car can go “from zero to sixty in 8 seconds”. This is a description of _________

Answer 21

average acceleration

Question 22

Suppose that a car traveling to the East (+x direction) begins to slow down as it approaches a traffic light. Which of the following statements is correct?

Answer 22

The car is accelerating, and its acceleration is negative

Question 23

Suppose that an object is moving with a constant velocity. Which of the following statements is correct?

Answer 23

The acceleration must be equal to zero.

Question 24

Can an object’s velocity change direction when its acceleration is constant? Support your answer with an example.

Answer 24

Yes, this is possible.

ex. a rock thrown straight up

Question 25

Under what condition is average velocity equal to the average of the object’s initial and final velocities?

Answer 25

The acceleration must be constant.

Question 26

Objects A and B both start from rest. They both accelerate at the same rate. However, object A accelerates for twice as long as object B. What is the distance traveled by object A compared to that of object B?

Answer 26

four times as far

use formula d= 1/2 at^2

Question 27

When an object is released from rest and falls in the absence of friction, which of the following is true concerning its motion?

Answer 27

Its acceleration is constant.

Question 28

Suppose a ball is thrown straight up. Choose the correct statement about the velocity and the acceleration when the ball reaches the highest point.

Answer 28

Its velocity is zero, and acceleration is not zero.

Question 29

A ball is thrown straight up, reaches a maximum height, then falls to its initial height. Choose the correct statement about the direction of the velocity and acceleration as the ball is coming down.

Answer 29

Both its velocity and it acceleration point downward.

Question 30

Suppose a ball is thrown downward in the absence of air resistance. Choose the correct statement concerning its acceleration.

Answer 30

Its acceleration is constant.

Question 31

Two objects are thrown from the top of a tall building. 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 31

They are traveling at the same speed.

Question 32

An object is moving with constant non-zero velocity in the +x axis. The position versus time graph of this object is ________

Answer 32

a straight line making an angle with the time axis

Question 33

An object is moving with constant non-zero acceleration in the +x axis. The position versus time graph of this object is _________

Answer 33

a parabolic curve

Question 34

An object is moving with constant non-zero acceleration in the +x axis. The velocity versus time graph of this object is _________

Answer 34

a straight line making an angle with the time axis

Question 35

The slope of a position versus time graph gives _________

Answer 35

velocity

Question 36

If the position versus time graph of an object is a horizontal line, the object is __________

Answer 36

at rest

Question 37

A boat can move at 30 km/h in still water. How long will it take to move 12 km upstream in a river flowing 6.0 km/h?

Answer 37

30 minutes

t = d/v
t = 12/ (30-6) = 0.5 hours

• we subtract 6 km/hr because we are moving against the current and therefore it will take us longer to reach destination*

Question 38

What must be your average speed in order to travel 350 km in 5.15 h?

Answer 38

68 hm/hr

= 350 km/ 5.15 hr

Question 39

A car travels 90 km/h. How long does it take for it to travel 400 km?

Answer 39

4.4 hrs

Question 40

An airplane is initially moving at 100 m/s when it begins to accelerate at the average rate of 15 m/s2. How much time does it take to increase its speed to 160 m/s?

Answer 40

4 seconds

160 - 100 = 60 m/s / 15 m/s^2 = 4 seconds

Question 41

A bullet moving horizontally to the right (+x direction) with a speed of 500 m/s strikes a sandbag and penetrates a distance of 10.0 cm before coming to a stop. What is the average acceleration, in m/s2, of the bullet after it strikes the sandbag?

Answer 41

-1.25 x 10^6

Question 42

A jet fighter plane is launched from a catapult on an aircraft carrier. It reaches a speed of 42 m/s at the end of the catapult, and this requires 2.0 s. Assuming the acceleration is constant, what is the length of the catapult?

Answer 42

42 m

v^2 = v-intial^2 + 2a (deltax)

Question 43

A car goes from 40 m/s to 80 m/s in a distance of 200 m. What is its average acceleration?

Answer 43

12 m/s

v^2 = v-intial^2 + 2a (deltax)

Question 44

A ball is thrown upward with an initial velocity of 19.6 m/s. What is its velocity after 3.00 s?

Answer 44

9.8 m/s downward

step 1.) find distance traveled and use -9.8 m/s for acceleration

step 2.) find velocity using velocity and displacement relation equation