# Physics

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