A car travels along a straight line at a constant speed of 41.5 mi/h for a
distance d and then another distance d in the same direction at another constant speed. The average velocity for the entire trip is 25.0 mi/h.
(a) What is the constant speed with which the car moved during the second
distance d?
Your response is within 10% of the correct value. This may be due to roundoff
error, or you could have a mistake in your calculation. Carry out all intermediate
results to at least four-digit accuracy to minimize roundoff error. mi/h
(b) Suppose the second distance d were traveled in the opposite direction; you forgot something and had to return home at the same constant speed as found
in part (a). What is the average velocity for this trip?
Your response differs significantly from the correct answer. Rework your solution
from the beginning and check each step carefully. mi/h
(c) What is the average speed for this new trip?
mi/h
2.–/3 pointsSerPSE8 2.P.013.My Notes |
A velocity—time graph for an object moving along the x axis is shown in the figure. Every division along the vertical axis corresponds to 2.00 m/s and each
division along the horizontal axis corresponds to 2.50 s.
(a) Plot a graph of the acceleration versus time.
This answer has not been graded yet.
(b) Determine the average acceleration of the object in the following time
interval t = 12.5 s to t = 37.5 s. m/s2
(c) Determine the average acceleration of the object in the following time
interval t = 0 to t = 50.0 s. m/s2
3.–/3 pointsSerPSE8 2.P.016.WI.My Notes | A particle starts from rest and accelerates as shown in the figure below.
(a) Determine the particle’s speed at t = 10.0 s. m/s
Determine the particle’s speed at t = 20.0 s? m/s
(b) Determine the distance traveled in the first 20.0 s. (Enter your answer to one
decimal places.)
m
4.–/3 pointsSerPSE8 2.P.017.MI.My Notes |
A particle moves along the x axis according to the equation x = 1.99 + 2.99t − 1.00t2,
where x is in meters and t is in seconds. (a) Find the position of the particle at t = 2.50 s. m
(b) Find its velocity at t = 2.50 s. m/s
(c) Find its acceleration at t = 2.50 s. m/s2
5.–/2 pointsSerPSE8 2.P.020.My Notes | Draw motion diagrams for the following items. (Do this on paper. Your instructor
may ask you to turn in your work.)
(a) an object moving to the right at constant speed
(b) an object moving to the right and speeding up at a constant rate
(c) an object moving to the right and slowing down at a constant rate
(d) an object moving to the left and speeding up at a constant rate
(e) an object moving to the left and slowing down at a constant rate
This answer has not been graded yet.
(f) How would your drawings change if the changes in speed were not uniform;
that is, if the speed were not changing at a constant rate?
This answer has not been graded yet.
6.–/5 pointsSerPSE8 2.P.021.My Notes | A parcel of air moving in a straight tube with a constant acceleration of –
4.10 m/s2 and has a velocity of 13.5 m/s at 10:05:00 a.m.
(a) What is its velocity at 10:05:01 a.m.?
m/s
(b) What is its velocity at 10:05:04 a.m.?
m/s
(c) What is its velocity at 10:04:59 a.m.?
m/s
(d) Describe the shape of a graph of velocity versus time for this parcel of air.
This answer has not been graded yet.
(e) Argue for or against the following statement: “Knowing the single value of an
object’s constant acceleration is like knowing a whole list of values for its
velocity.”
This answer has not been graded yet.
7.–/3 pointsSerPSE8 2.P.024.MI.My Notes | We investigated a jet landing on an aircraft carrier. In a later maneuver, the jet
comes in for a landing on solid ground with a speed of 95 m/s, and its
acceleration can have a maximum magnitude of 5.52 m/s2 as it comes to rest.
(a) From the instant the jet touches the runway, what is the minimum time
interval needed before it can come to rest?
s
(b) Can this jet land on a small tropical island airport where the runway is 0.800
km long?
Yes No
(c) Explain your answer.
This answer has not been graded yet.
8.3/5 points | Previous AnswersSerPSE8 2.P.027.My Notes | A speedboat travels in a straight line and increases in speed uniformly
from vi = 12.5 m/s to vf = 41.5 m/s in a displacement Δx of 150 m. We wish to find the time interval required for the boat to move through this displacement.
(a) Draw a coordinate system for this situation. (Do this on paper. Your
instructor may ask you to turn in this work.)
(b) What analysis model is most appropriate for describing this situation?
particle under constant speed particle under constant acceleration particle in
equilibrium
(c) From the analysis model, what equation is most appropriate for finding the
acceleration of the speedboat?
vf = vi + at
Δx = vi + 1 2
at2
vf2 = vi2 + 2aΔx
(d) Solve the equation selected in part (c) symbolically for the boat’s acceleration in terms of vi, vf, and Δx.
a =
(e) Substitute numerical values to obtain the acceleration numerically.
m/s2
(f) Find the time interval mentioned above.
s
9.1/4 points | Previous AnswersSerPSE8 2.P.033.My Notes | An object moves with constant acceleration 4.10 m/s2 and over a time interval
reaches a final velocity of 12.8 m/s.
(a) If its initial velocity is 6.4 m/s, what is its displacement during the time
interval?
m
(b) What is the distance it travels during this interval?
m
(c) If its initial velocity is -6.4 m/s, what is its displacement during the time
interval?
Your response differs from the correct answer by more than 10%. Double check
your calculations. m
(d) What is the total distance it travels during the interval in part (c)?
Your response differs from the correct answer by more than 10%. Double check
your calculations. m
10.–/4 pointsSerPSE8 2.P.038.My Notes | An attacker at the base of a castle wall 3.90 m high throws a rock straight up
with speed 9.00 m/s from a height of 1.70 m above the ground.
(a) Will the rock reach the top of the wall?
Yes No
(b) If so, what is its speed at the top? If not, what initial speed must it have to
reach the top?
m/s
(c) Find the change in speed of a rock thrown straight down from the top of the
wall at an initial speed of 9.00 m/s and moving between the same two points.
m/s
(d) Does the change in speed of the downward-moving rock agree with the
magnitude of the speed change of the rock moving upward between the same
elevations? Explain physically why it does or does not agree.
This answer has not been graded yet.
11.0/1 points | Previous AnswersSerPSE8 2.P.041.WI.My Notes | A ball is thrown directly downward with an initial speed of 8.65 m/s from a
height of 29.6 m. After what time interval does it strike the ground?
You know the initial velocity, the distance and the acceleration. Which equation
in Table 2.2 will allow you to find the time? You may need to use the quadratic
equation. s
12.–/1 pointsSerPSE8 2.P.042.My Notes |
The height of a helicopter above the ground is given by h = 2.80t3, where h is in meters and t is in seconds. At t = 1.70 s, the helicopter releases a small mailbag. How long after its release does the mailbag reach the ground?
s
13.2/4 points | Previous AnswersSerPSE8 2.P.043.MI.My Notes | A student throws a set of keys vertically upward to her sorority sister, who is in a
window 2.00 m above. The second student catches the keys 2.30 s later.
(a) With what initial velocity were the keys thrown?
magnitude Your response differs from the correct answer by more than 100%. m/s
direction
(b) What was the velocity of the keys just before they were caught?
magnitude The correct answer is not zero. m/s
direction
14.–/3 pointsSerPSE8 2.P.048.My Notes |
Question Part
Points
Submissions Used
A student drives a moped along a straight road as described by the velocity
versus time graph in the figure. The divisions along the horizontal axis
represent 1.0s and the divisions along the vertical axis represent 2.0 m/s.
Sketch this graph in the middle of a sheet of graph paper. (Do this on paper.
Your will need it to do part (a) and (b).)
(a) Directly above your graph, sketch a graph of the position versus time,
aligning the time coordinates of the two graphs. (Do this on paper. Your
instructor may ask you to turn in your work.)
(b) Sketch a graph of the acceleration versus time directly below the velocity-
versus time graph, again aligning the time coordinates. On each graph, show the
numerical values of x and ax for all points of inflection. (Do this on paper. Your instructor may ask you to turn in your work.)
(c) What is the acceleration at t = 6.0 s? m/s2
(d) Find the position (relative to the starting point) at t = 6.0 s. m
(e) What is the moped’s final position at t = 9.0 s? m
15.–/5 pointsSerPSE8 2.P.053.MI.My Notes |
Question Part
Points
Submissions Used
An inquisitive physics student and mountain climber climbs a 54.0-m-high cliff
that overhangs a calm pool of water. He throws two stones vertically downward,
1.00 s apart, and observes that they cause a single splash. The first stone has an
initial speed of 1.88 m/s.
(a) How long after release of the first stone do the two stones hit the water?
s
(b) What initial velocity must the second stone have if the two stones are to hit
the water simultaneously?
magnitude m/s
direction
(c) What is the speed of each stone at the instant the two stones hit the water?
first stone m/s
second stone m/s
