1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Imposing Coordinates

  1. Jan 7, 2009 #1
    1. The problem statement, all variables and given/known data

    Eriks disabled boat is floating at a stationary location 3 miles East and 2 miles North of Kingston. A ferry leaves Kingston heading due East towards Edmonds at 12mph. Erik leaves the sailboat in a dingy heading due South at 10ft/sec (hoping to intercept the ferry). Edmonds is 6 miles due East of Kingston.

    a) Compute Eriks spead in mph and the ferrys speed in ft/sec.
    b) Impose a coordinate system of Erik and the ferry. What are Eriks and the ferrys locations at time 0, 30sec, 7min, and 1 hour? What are the distances between them at each time-point?
    c) Explain why Erik misses the ferry.
    d) After 10 minutes a Coast Guard boat leaves Kingston heading due East at a speed of 25ft/sec. Will the Coast Gaurd boat catch the ferry before it reached Edmonds? Explain.

    2. Relevant equations
    distance = rate X time
    d=sqrt (x2-x1)^2 - (y2-y1)^2

    3. The attempt at a solution

    a) Eriks speed is 10ft/sec or 6.818 mph
    The ferrys speed is 12mph or 17.604 ft/sec
    b)Eriks orgin is (3,2)
    Ferry orgin is (0,0)

    I am confused with how to use the coordinates to calculate their positions at certain time-points.

    I think to find the distances between them at the given time-points I use the following equations and substitute them into the distance formula:
    Erik: (3, 2-6.818) Ferry: (12,0)

    Any help is appreciated!
  2. jcsd
  3. Jan 7, 2009 #2


    Staff: Mentor

    As you pointed out, d = r*t, so you need to represent Erik's and the ferry's positions at time t. To get you started, Erik's position at time t (in hours) is (3, 2 - 6.818*t). You need to find the ferry's position at time t and calculate the distance between these points. Presumably, at some value of t, the distance will be 0.
  4. Jan 7, 2009 #3


    Staff: Mentor

    By the way, are you at EdCC or maybe ShorelineCC?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook