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Homework Help: Vectors in Physics

  1. Sep 17, 2007 #1
    1. An off-roader explores the open desert in her Hummer. First she drives 25 degrees west of north with a speed of 6.5 km/h for 15 minutes, then due east with a speed of 13 km/h for 7.5 minutes. She completes the final leg of her trip in 22 minutes.

    a) What is the direction and speed of travel on the final leg? (Assume her speed is constant on each leg, and that she returns to her starting point at the end of the final leg.)

    Theta= _______ degrees south of west

    b) Express your answer using two significant figures.

    v= ________ km/h

    Displacement Vector: Delta R; Delta R= Rf - Ri
    Velocity Vector: POints in the direction of motion and has a magnitude equal to the speed.
    Acceleration Vector: The acceleration vector indicated how quickly and in what direction the velocity is changing. It need not point in the direction of motion.
    Velocity of Object 1 Relative to Object 3
    V13= V12 + V23 where object 2 can be anything
    Reversing the subscripts on a velocity
    V12= -V21

    3. I am really lost on this problem. I began by drawing a graphical representation. If the off-roader heads 25 degrees west of north, it would be 25 degrees to the left of the 90 degrees on the graph, which would equate to 90 deg + 25 deg. = (+) 115 degrees. I think you have to get a delta V (velocity) by subtracting Vf - Vi. I am really lost at this point. A general outline of how to approach this problem would be great!
    Last edited: Sep 17, 2007
  2. jcsd
  3. Sep 17, 2007 #2


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    Staff Emeritus
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    Gold Member

    Welcome to PF btchrist. Could I just ask you to re-post the question as you have it written down. It is a little unclear what must be done to find the final leg of the journey. Secondly, when posting any value please supply the appropriate units with it. It makes things a lot clearer and easier to deal with as it saves guessing what numbers are.
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