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Standing and traveling waves (MC)

Page history last edited by Joe Redish 9 years, 7 months ago

9.2.P5

 

In the figure at the right is shown three graphs of the shapes of the same taut elastic string in three different circumstances, labelled A, B, and C. In some of the problems below, the string represents a guitar string, tied down at both ends, while in others, it is part of a very long telephone wire whose ends are not shown. Be careful to note which is which for each problem! The string is light enough that the effects of gravity can be ignored. In each case, the bit of string at the position x = 23 cm is painted blue. For each of the 5 problems below, put all the correct answers in the box at the right of the problem.

 

1. Suppose the three graphs all represent the same string, tied down at x = 0 and x = 70 cm, and at the same tension. What can you say about the three frequencies of oscillation?

  1. Situation A has the highest frequency.
  2. Situation B has the highest frequency.
  3. Situation C has the highest frequency.
  4. The three frequencies are all the same.
  5. You can’t say anything from the information given.

 

2. Suppose the three graphs all represent the same string, tied down at x = 0 and x = 70 cm, but their tensions have been adjusted so that all three situations are all oscillating at the same frequency. What can you say about the tensions in the three cases?

  1. You can’t adjust the tensions to make the frequencies the same since the wavelengths are different.
  2. The tension in string C is the greatest.
  3. The tension is string A is the greatest.
  4. All three tensions are the same.
  5. You can’t say anything from the information given.

 

3. Suppose that graph C represents the string, tied down at x = 0 and x = 70 cm, under tension. What can you say about the acceleration of the blue bead in case C at the instant shown?

  1. It is upward.
  2. It is downward.
  3. It is 0.
  4. You can’t say anything from the information given.

 

4. Suppose that graph C represents part of a long wire, under tension, and is showing a left traveling wave at a particular instant. What can you say about the velocity of the blue bead in case C at the instant shown?

  1. It is upward.
  2. It is downward.
  3. It is 0.
  4. You can’t say anything from the information given.

 

5. Suppose that graph C represents part of a long wire, under tension, and is showing a left traveling wave at a particular instant. What can you say about the acceleration of the blue bead in case C at the instant shown?

  1. It is upward.
  2. It is downward.
  3. It is 0.
  4. You can’t say anything from the information given.

 

 

Joe Redish 8/15/12

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