Unit: waves
Year: 1993 Question#: 40
Question: The periodic wave in the diagram below has a frequency of 40. hertz.
What is the speed of the wave?
(1 ) 13 m/s
(2 ) 27 m/s
(3 ) 60 m/s
(4 ) 120 m/s
What is this question really asking?
Explanation by: Liz M.
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Answer 1
13 m/s
INCORRECT
To find the speed of a wave you need the formula v= (frequency)(wavelength). The 3.0m that is given to you is twice the wavelength. You probably used the formula wrong and made it v= (frequency)/(wavelength). You probably also used the 3.0m instead of 1.5m (one cycle). Your answer would come out to be approximately 13 m/s. Incorrect. return to top
Answer 2
27 m/s
INCORRECT
To find the speed of the wave you need the formula v=(frequency)(wavelength). You knew that 3.0 was twice the wavelength but you used the formula incorrectly and plugged the correct numbers into the incorrect formula [ v=(frequency)/(wavelength). This would give you an answer of about 27m/s. Incorrect. return to top
Answer 3
60m/s
CORRECT
You knew that the given length of the wave (3.0m) was 2 periods of a wave so you divide it in half getting 1.5m as wavelength. You plugged in that number along with the given 40hz. into the formula v=(frequency)(wavelength)
v=(40hz)(1.5m)=60m/s. Correct. return to top
Answer 4
120m/s
INCORRECT
You plugged the wrong numbers into the right formula [v=(wavelength)(frequency)]. You neglected to realize that the given wavelength of 3.0m is 2 periods of a wave and must be divided in half before plugged into formula. You did this:
v= (40hz)(3.0m)
v= 120m/s
Incorrect. return to top
What's this question really asking?
The question is asking if the student knows how to apply the speed of a wave formula to the given information. It is really checking to see if the student knows that the 3.0m is twice the wavelength and needs to be divided. Otherwise it is simply a case of finding the formula in the reference table and plugging in the numbers. return to top
