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Homework Help: Questions Galore

  1. Nov 26, 2003 #1
    My last exam was given to me ungraded because i think I did so poorly on it. I think i did a good job on the True or False and the Multiple Choices. I think the weak point was in the questions that involved me applying the many subjects i had to learn. but here are section 1 of the questions I "suspect" are wrong:

    Dogs cool their bodies by sticking out their tongues and panting, which causes saliva in their mouth and respiratory system to evaporate. The normal breathing rate of a dog is about 30 breaths a minute. The respiratory system of a medium-sized dog has a resonance frequency of about 5Hz.

    A. In breaths per minute, how fast would a dog be breathing if it were to pant at the natural resonance frequency of its respiratory system? My Answer: He would have to breath 5 breaths a second.

    B. The greater the amplitude of the vibration of the respiratory system, the greater the expanstion and contraction of that system -- which means that more air enters the respiratory tract. Why do you think dogs pant at the resonant frequency of their respiratory systems? My Answer: Theyll cool off more when they go against their natural frequency.

    Next two questions are on the subject of colors.

    1. Childrens's tops are usually multi-colored, made of all the colors of the rainbow, yet when they spin they look white. Why?
    My Answer: Because when it spins, it joins all the colors in the spectrum making a white appearance (or white light).

    2. Many Churches and elegant Victorian houses have stained glass windows, made up of designs with transparent colored glass. What produces the color in the transparent glass? Why are different parts of the window different colors? My Answer:The windows are designed to absorb all the colors of white light, except for a certain color, which comes to be to the set pigment, and this goes for all the other parts of the windows.
  2. jcsd
  3. Nov 26, 2003 #2


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    You put the wrong units.

    The wording of this equestion is very bad. I don't even understand exactly what it is asking.

    pretty much

    That's exactly right.
  4. Nov 27, 2003 #3
    1.The greater the amplitude of the vivration of the respiratory system, the greater the expansion and contraction of that system - - which means that more air enters the respiratory tract, Why do you think dogs pant at the resonant frequency of thier respiratory systems?

    2.Why are Polaroid sunglasses, which are good for blocking out glare, not recommended for viewing the sun during a solar eclipse? My Answer: Polaroid sunglasses only work with horizantally vibrating light, not in other directions.

    3.Musicians must "warm up" their instruments before a concert. From what you've learned in this unit, do you think that air temperature affects the pitch of musical instruments? If it does, what effect does it have? Give a reason for your answer. My Answer: ? -- i put that because I only know that sound can transmit better in warm air, I know nothing about pitch.

    4.If a person breaths thirty times in a minute, what is the period in seconds and the frequency in hertz of her breaths? Show your calculations. My Answer: Each breath takes two seconds

    Frequency = 30/period = 30/60 = 30/60 = 2 Hz
    Period = 60/frequency = 60/30 = 60/30 = 2 seconds

    5.Olympic swimmers can swim at a speed of 1.7 m/s. If an olympic swimmer were swimming in the ocean on day when the wavelength of the waves was 20 m and the frequency was 1 Hz, would the swimmer be able to swim fast enough to avoid being lifted by a wave? Show your calculations. My Answer:

    wave speed = frequency x wavelength
    20 m/s = 1 Hz x 20 m

    No he wouldn't be able to swim fast enough to avoid being lifed by the wave because the wave speed is so powerful.

    6.Sound travels around 340 m/s in air. If a bat squeaks and hears the echo of its squeak return to ti 6 seconds later, how far away is the insect which the bat's squeak encountered? Show your calculations.

    My Answer: 340 m/s x 6s = 2040 meters

    7.Two sounds, one of 200 Hz and one of 194 Hz, occur at the same time.
    What beat frequency do you hear? Show your calculations. My Answer: The two sounds would produce 6 beats a second, and it would be heard around 197Hz.

    200 Hz - 194 Hz = 6 Hz
  5. Nov 28, 2003 #4
    #4) You got the period right, but frequency is equal to 1/Period or whatever (in this case breaths) per second so 30/60 is right but 30/60 isn't 2 it's 1/2 same as what you would have gotten with 1/Period.

    #5) I think you got that one right, but you should have just told him that they would have dove around the waves. I live 1500 miles from both the pacific and the atlantic and I know that.

    #6) You needed to remember that the sound has to go there and back so it actually travels twice the distance to the object so half of your answer would have been right.

    #7) You got the beat frequency of 6 Hz right.

    Bored CSMPhysicist
  6. Nov 28, 2003 #5


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    Polaroid glasses mainly filter out light reflected off other surfaces. Polaroid glasses do not effectively filter direct light. Staring at the sun with polaroid glasses won't protect your eyes.

    The pitch of sound is determined by the frequency of the sound. The speed of the sound is given by the formula V = 331 * sqrt(T/273). A general equation for all waves is V = wavelength * frequency. The wavelength of the waves coming from the instraments is determined by the tension in the strings and the length of the strings. This means that temperature only affects the frequency. Higher temperature means the instraments will generate a sound with a higher frequency (higher pitch).

    The unit for frequency is 1/s. That makes it easy to find how to write the equation
    f = 30/60s
    f = 0.5/s
    f = 0.5Hz

    T = 1/f
    T = 1/0.5
    T = 2s


    d = vt/2
    d = (340)(6)/2
    d = 1020m
  7. Nov 28, 2003 #6

    Still, I don't know where the '2' came from in that last question? Am I suppose to have a fore knowledge of these things?
  8. Nov 28, 2003 #7


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    It's divided by 2 because it goes there and back.

    They assume you know that.
  9. Nov 28, 2003 #8
    Physics is Nonsense to me, I looked over this section of the book THROUGHLY , and I still doesnt compute in my head. So forgive me if my questions seems very stupid. Thank You
  10. Nov 28, 2003 #9
    was csmines right about the fifth question?
  11. Nov 28, 2003 #10
    does this look correct?

    frequency = period / 30 = 60 / 30 = 1 / .5 Hz = .5hz?
  12. Nov 28, 2003 #11


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    Your answer on the fifth question was correct. His answer is technically right but it's the "smart ass" answer that angers teachers. Don't ever put the smart ass answer.
  13. Nov 28, 2003 #12


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    math errors.
    First of all, 1/0.5 is 2,not 0.5

    Second thing, as a general rule, you should simplify to whole numbers. For example, 60/30 should be simplified as 2/1. While 1/0.5 is technically correct, it doesn't follow the standard of expressing fractions as whole numbers over whole numbers.
  14. Nov 28, 2003 #13
    Sorry about the "smart ass" answer,
    after having studied physics for 6 or 7 years now I realized that you've got to have a little fun with the teachers. I apologize if my answer confused you, I did however begin my comment with the statement "I think you're right." Won't happen again.

  15. Nov 28, 2003 #14
    so should it be like you wrote it?:


  16. Nov 28, 2003 #15
    You're on the money now.
  17. Nov 28, 2003 #16


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    You can have fun with your teachers but don't look for loopholes on tests... My math teacher used to tell stories of this one smart ass kid who would always find a loophole on the test and assignments so he wouldn't have to think or do anything. Here are some examples:

    1. With interval notation, "(" and ")" mean not inclusive. (5,9) means it is BETWEEN 5 and 9 and cannot be equal to 5 or 9. The teacher assigned some questions to be handed in and he wrote on the board the page number then he put (1,2). He meant for students to do questions 1 and 2. The smart ass student had the excuse "you had the rounded brackets and since there is no integer between 1 and 2, you assigned no homework".

    2. On one particular test, there was a question about a BALL falling at some acceleration and you had to find the distance over some time for the ROCK using calculus; no equations from physics class. Everybody knew about the typo in the question and just ignored the error, but the smart ass kid put something like "the rock has no change over time because it was a ball falling, not a rock".

    The teacher absolutely hated that kid.
  18. Nov 28, 2003 #17
    There is certainly a difference between writing out a loop hole answer because you want to piss someone off or writing out a loop hole answer because you don't know the answer and want to laugh at your fault. I have yet to have a teacher hate me; if you are jesting in good humor I've always found that creativity is appreciated. People who are always serious and hardnosed have a tendency to burn out much faster, so have a sense of humor. Sounds like the kid you knew was thumbing his nose as opposed to trying to humor his teacher.
  19. Nov 28, 2003 #18
    I understand, the last thing i want to do is act in a way that would make my teacher angry. Im desperately trying to learn and finish these questions so that i can finish high school. Because of my inability to undertand physics to the fullest, its taking me slower to finish than I had planned. So thats why I came to this Homework help forum.
  20. Nov 28, 2003 #19
    can you show me how the fifth question looks like again? how does the answer make sense?
  21. Nov 28, 2003 #20
    7.Two sounds, one of 200 Hz and one of 194 Hz, occur at the same time.
    What beat frequency do you hear? Show your calculations. My Answer: The two sounds would produce 6 beats a second, and it would be heard around 197Hz.

    200 Hz - 194 Hz = 6 Hz

    does that look ok?
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