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Motion on incline

  1. Oct 7, 2006 #1
    problem: A ball is allowed to roll from rest down an inclined plane, and the distances are marked every 2.5s. if the second mark is made 1.5m from the starting point, where is the first mark?

    where is the fourth mark?

    well i made a velocity vs. t chart and the velocity of it is 0.6 then ifound the velocity of ech number on my graph but iwas told my answer was wrong. can you help me please.
     
    Last edited: Oct 7, 2006
  2. jcsd
  3. Oct 7, 2006 #2
    Can you put your homework questions in the homework section please.
     
  4. Oct 7, 2006 #3
    how this is only my second time?
     
  5. Oct 7, 2006 #4
    There is a thread for homework help on the main page. It's the second one down from the top.
     
  6. Oct 7, 2006 #5

    arildno

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    Let indices 1,2 indicate different instants and the associated distances travelled. Thus, using your distance formula for two different times, we've got the formulae:
    [tex]d_{1}=\frac{a}{2}t_{1}^{2} (1), d_{2}=\frac{a}{2}t_{2}^{2}(2)[/tex]
    where a is the acceleration.

    Now, divide these equations with each other:
    [tex]\frac{d_{1}}{d_{2}}=\frac{\frac{a}{2}t_{1}^{2}}{\frac{a}{2}t_{2}^{2}}\to\frac{d_{1}}{d_{2}}=\frac{t_{1}^{2}}{t_{2}^{2}}\to[/tex]
    [tex]\frac{d_{1}}{d_{2}}=(\frac{t_{1}}{t_{2}})^{2}[/tex]

    agreed?
     
  7. Oct 7, 2006 #6
    i'm sorry i don't understand any of that
     
  8. Oct 7, 2006 #7

    arildno

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    Nonsense.
    Start studying it from line 1, and report back precisely what you don't understand!
     
  9. Oct 7, 2006 #8
    where do you get 1,2
     
  10. Oct 7, 2006 #9

    arildno

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    I give two NAMES to two different instants!!
    Am I not allowed to give names to quantities? :confused:

    Should I give them the same name, perhaps??
     
  11. Oct 7, 2006 #10
    so the 1st equation would be 1.5=a(2.5)^2 right?
     
  12. Oct 7, 2006 #11

    arildno

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    If you want [itex]t_{1}[/itex] to be interpreted as 2.5, yes.
     
  13. Oct 7, 2006 #12
    ok for this i get 0.24, but what is the second instants the fourth mark?
     
  14. Oct 7, 2006 #13

    arildno

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    Look, do you understand how I got the equation:
    [tex]\frac{d_{1}}{d_{2}}=(\frac{t_{1}}{t_{2}})^{2}[/tex]
     
  15. Oct 7, 2006 #14
    not really, i do understand the 1,2 now but i don't see where you get the second instants. this problem just really confuses me i'm sorry.
     
  16. Oct 7, 2006 #15

    arildno

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    Do you understand that I can divide one equation with the other?
     
  17. Oct 7, 2006 #16
    so you took d=a(t)^2 and divided it by itself? with different subscripts?
     
  18. Oct 7, 2006 #17
    so you took d=a(t)^2 and divided it by itself to get D(1)/D(2)=(t(1)/t(2))^2 right?
     
  19. Oct 7, 2006 #18
    sorry i didn't see it come up i typed it again ignore the first on please.
     
  20. Oct 7, 2006 #19

    arildno

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    Correct!
    Do you agree I am allowd to do that?
     
  21. Oct 7, 2006 #20
    yes, but is the first instants the first mark and the second instants the second mark?
     
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