TBR Physics - Doppler question (easy)

[ilovemedi]

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Question #11, passage 2.

If an ultrasonic imager operates at a frequency of 157,000Hz, what is the SMALLEST object the image could detect?
A) 1mm
B) 1cm
c) 1m
d) no min size.

Answer: B.
I get we use v=w.l * frequency. rearrange for w.l=v/f and f = 157,000Hz then what? What's our velocity? it's not at all given. They put v as 1570m/s.. where the heck did that come from? The passage does say that v = 1570 m/s for FLESH, but this has nothing to do w/ the human body.. it can be an ultrasonic imager for anything?

 

[ilovemedi]

bump.

 

[whathappened1]

i'm stuck on this too! anyone get why they put that as velocity?

 

[makingthejump]

I just studied this topic today, having only 1 variable does not allow for answer to be found UNLESS the passage infers the velocity somewhere. Seems like an error, but I agree to use velocity=frequency x wavelength which is WL=v/f.

 

[stickywebz]

since its ultrasonic would the speed be the speed of sound? @ 340 m/s?

 

[ilovemedi]

Yeah, but they said the speed is v = 1570 m/s which is listed for the speed in flesh. I was just confused why they chose flesh as the material, since I thought it mean the smallest object detected in terms of anything..