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Average Velocity

  1. Oct 23, 2008 #1
    1. The problem statement, all variables and given/known data
    A meteor streaking through the night sky is located with radar. At point A its coordinates are (5.20km, 1.20km), and 1.18 s later its has moved to point B with coordinates (6.24, 0.915).


    1. Find the magnitude of its average velocity between these two points.

    2. Find the direction of its average velocity between these two points. ( degree is counterwise from +x axis.)

    2. Relevant equations
    No equations were given

    3. The attempt at a solution

    First i added all the x components and squared it. Then I added all the y components and squared it. Took the square root and got 8.2616

    I took the 8.2616 and divided by the time of 1.18seconds

    But the answer is wrong. :( !!


    Help please~
    Teababy
     
  2. jcsd
  3. Oct 23, 2008 #2

    Redbelly98

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    I would try drawing a figure, perhaps on some graph paper, and locate the two given points on the figure. Draw the right triangle that is appropriate for figuring out the distance between the points, and take it from there.
     
  4. Oct 23, 2008 #3
    to find the distance it covers, you subtract the x coordinates and square the result. do the same for the y coordinates. add the result and then find its square root.
     
  5. Oct 23, 2008 #4
    I subtracted x2-x1 and added it with y2-y1 and took the square root

    my magnitude came out to be 1.0703 but it was wrong
     
  6. Oct 23, 2008 #5
    i get 1.0783. then divide it by 1.18 s, then the answer is ........ km/s. if you need to express the answer in other unit, then convert the unit.
     
  7. Oct 23, 2008 #6
    You have to realize that the problem you are dealing with is with a coordinate system. So to find the distance it covers in the x direction you would do as you did and subtract the two. Same for y.

    Knowing that, use a triangle and Pythagorean's theorem to find the magnitude.

    -Sorry guess you already did all that, I didn't check your answer I thought you forgot to square it.
     
  8. Oct 23, 2008 #7
    First of all thank you Redbelly98, Leong, and Sheneron for all your help. It's very much appreciated.


    I got the right answer which came out to be 0.914 =D

    now on to the 2nd part:

    2. Find the direction of its average velocity between these two points. ( degree is counterwise from +x axis. )

    what i did was take the inverse tangent of -0.242/0.881 = 12.41

    I also tried -12.41 degree and it was also wrong

    :(
     
  9. Oct 23, 2008 #8
    I would try sketching a figure and locate the two given points on the figure. Draw the right triangle that is appropriate for figuring out the angle.
     
  10. Oct 23, 2008 #9
    find the inverse tangent is right.
    the two values are wrong and irrelevant.
     
  11. Oct 23, 2008 #10
    I sketched a right triangle, and I for the height i added up the y-components and for the x i added up all the x-components. the hypot i put the magnitude.

    So to find the angle, does it mean i can use either cos, sin, and tangent?
     
  12. Oct 23, 2008 #11
    oh wait! i posted before i saw your responds. I'll take a look again at my numbers.
     
  13. Oct 23, 2008 #12
    figure attached.
     

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  14. Oct 23, 2008 #13
    I did inverse tangent of sum of y's over the sum of x's. Thus: tangent-1 (2.125/11.24) = 10.70 .. am i doing this right?
     
  15. Oct 23, 2008 #14
    I'm sorry I'm new here. How do i approve your pending graph?
     
  16. Oct 24, 2008 #15
    you can't. only the moderators can.
     
  17. Oct 24, 2008 #16
    i think u will just have to wait.
     
  18. Oct 24, 2008 #17
    no it is wrong too.
     
  19. Oct 24, 2008 #18

    Redbelly98

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    It's a mistake to take the sums here. Look at your figure again ... the side along x is no where close to 11 units long. Think more carefully about how to calculate that side length. Then do the same for the y-direction side.
     
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