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Homework Help: Vibrations and Waves

  1. Jun 9, 2004 #1
    Need help please....I am having trouble with this question.... :confused:

    A mass m at the end of a spring vibrates with a frequency of 0.88 Hz. When an additional 600 g mass is added to m, the frequency is 0.60 Hz. What is the value of m?
  2. jcsd
  3. Jun 9, 2004 #2
    A 25.0 g bullet strikes a 0.600 kg block attached to a fixed horizontal spring whose spring constant is 6.70 * 10^3 N/m and sets it into vibration with an amplitude of 21.5 cm. What was the speed of the bullet before impact if the two objects move together after impact? :eek:
  4. Jun 9, 2004 #3
    This seems very easy, but no matter what I do it doesn't give me the right answer....how do I do this?????? :frown:

    A cord of mass 0.50 kg is stretched between two supports 27 m apart. If the tension in the cord is 145 N, how long will it take a pulse to travel from one support to the other?
  5. Jun 9, 2004 #4
    You have the tension and the mass per unit length. There is a formula in your textbook that will provide the speed of the wave given those values.

    How do you know the right answer is THE right answer?
  6. Jun 10, 2004 #5
    alright. the speed of a wave in a string is equal to the root of the tension over the linear mass density. so v=(145N/(0.5kg/27m))^1/2. this gives you an anwser for velocity that is about 88.5 m/s so the time required for a pulse to travel the distance between the two supports is 27m/88.5m/s=0.305s.
  7. Jun 10, 2004 #6
    the frequency is proportional to one over the root of the mass. I think you should be able to figure it out from here.
  8. Jun 10, 2004 #7
    try conservation of energy...

    also, I believe there is a separate section for homework help...
  9. Jun 10, 2004 #8


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    Not only is there a homework section but you will find that it is much easier for others to respond if either you create a single thread for all questions or title each thread differently. Multiple threads with the same title create nothing but confusion.
  10. Jun 10, 2004 #9


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    What is the relation between frequency and
    Spring constant and mass

    Note that you have been given 2 unknowns, spring constant k and original mass m.

    The two expressions for the frequency give you two equations in these two unknowns.
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