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Homework Help: A van is travelling north - Vector question.

  1. Mar 14, 2008 #1
    Hi, I have just started A-level physics and bought the Letts AS/A2 study guide from which I am working. However I have gotten stuck right at the beginning! Please can someone figure this out with an explanation? Also any recommendations on good but concise textbooks? I was thinking of buying Physics for Dummies.

    1. A van is travelling north at a speed of 28ms. After turning a corner it is heading 40 degrees east of north at 25ms. Work out the change in velocity of the van

  2. jcsd
  3. Mar 14, 2008 #2


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    Velocity is a vector …

    Hi shamswahid! Welcome to PF! :smile:

    The question gives you two velocities (speed-plus-direction), and asks you to find the difference.

    Velocity is a vector.

    What that means (among other things) is that you can combine them using vector diagrams (usually triangles).

    So draw the triangle (roughly), and calculate the unknown side and angle! :smile:
  4. Mar 14, 2008 #3


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    Hi Shams! :smile:

    No, you have to do the work!

    Draw the triangle: one side will be 28, straight up, and one side will be 25 at an angle of 40º to it.

    You can find the length of the third side either by using x and y coordinates, or by using the trig formula:
    [tex]A^2\,=\,B^2\,+\,C^2 -2BC\,cosa\,.[/tex]​

    (Using x and y coordinates is probably easier.)

    Have a go! :smile:
  5. Jan 15, 2011 #4
    Well i tried using pythagoras 252=282+x^2.
    but i cannot work out x.
    what did i do wrong?
    please help.
  6. Jan 15, 2011 #5


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    uhh? what does Pythagoras have to do with it? :confused:

    either use the trig formula, or use x and y coordinates
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