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Velocity of a cursor physics

  1. Jun 27, 2009 #1
    In the position shown in Figure, the cursor B moves to the left with a speed of 150 mm/s. Find (a) the velocity of the A (b) the velocity C portion of the cable (c) the velocity of C on B

    Answer:
    (a) 300 mm/s
    (b) 600 mm/s
    (c) 450 mm/s
     

    Attached Files:

  2. jcsd
  3. Jun 27, 2009 #2

    Pengwuino

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    Re: Velocity

    Please show some work first. We are not here to do your homework for you.
     
  4. Jun 27, 2009 #3
    Re: Velocity

    Because of Pulleys, I think

    2Vb + 4Va = 0

    But not find the answer
     
  5. Jun 27, 2009 #4
    Re: Velocity

    People can't help you unless you post your attempted solutions. It's a place where people help you on homework, not do your homework for you.
     
  6. Jun 28, 2009 #5
    Re: Velocity

    But I do not know how to solve this problem. As I will show something is not understood the problem ?
     
  7. Jun 28, 2009 #6

    tiny-tim

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    Hi Apprentice123! :wink:
    Tell us your reason (in words) for thinking it's 2Vb + 4Va = 0, and then we can see what went wrong, and we'll know how to help. :smile:
     
  8. Jun 28, 2009 #7
    Re: Velocity

    I thought the speed at B is 1 pulley (2 * speed) and speed in A has 2 pulleys (4 * speed)
     
  9. Jun 28, 2009 #8

    tiny-tim

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    ?? i've no idea what you're talking about :confused:

    it's the number of strings that matters

    Hint: if A moves distance x to the left, how much longer do the two strings on the right of A get? :smile:
     
  10. Jun 28, 2009 #9
    Re: Velocity

    Yes. I think

    B (have 2 strings)
    A (have 4 strings)

    2x = 150
    4x = 300 Ok.

    But the C portion (have 1 string) x = 75 not the answer
     
  11. Jun 28, 2009 #10

    tiny-tim

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    No, A has 3 strings (1 on the left, 2 on the right), and only 2 of them are on a pulley

    Anyway, answer my question …if A moves distance x to the left, how much longer do the two strings on the right of A get? :smile:
     
  12. Jun 28, 2009 #11
    Re: Velocity

    If A have strings (1 on the left and 2 on the right) move x to left and 2x to right. It is ?
     
  13. Jun 28, 2009 #12

    tiny-tim

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    It is very difficult to understand your English :redface:

    "If A moves a distance x to the left, then each string on the right must get x longer, so the two strings together get 2x longer"

    ok, call the length of the string on the left D, and the length of each string on the right E

    then C + D + 2E = constant,

    and D + E = … ? :smile:
     
  14. Jun 28, 2009 #13
    Re: Velocity

    Thank you.
    A)
    1 a left
    two for right
    Va = 2 x 150 = 300 mm/s

    B)
    1 a left
    2x2 for right
    Vc = 4 x 150 = 600 mm/s

    C)
    (2 + CB cable) = 3
    Vc/b = 3 x 150 = 450 mm/s
     
  15. Jun 28, 2009 #14

    tiny-tim

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    Yes, your answers to (a) and b) are correct, but I have no idea how you got them.

    In the exam, to get full marks, you will need to explain clearly how you get your answers.
    Unfortunately, I do not understand what question (c) means, so I can't say whether your answer is correct … what is "the velocity of C on B"? … can you please explain it? :smile:
     
  16. Jun 28, 2009 #15
    Re: Velocity

    The speed of the string C on B
     
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