BMAT 2020 - Physics Q

I don’t know why this calculation is a bit confusing could someone show me the breakdown?


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Hi!
there’s a bit of trap in this question it says the object is 750m in front of submarine and it takes a total of 1.00 s for pulse to return back to the submarine so the total distance travelled by the pulse equals 750m during departure and 750m when it returns back equalizing it to 1500m.
Now, we can calculate the speed of the pulse using the relation d=speed x time=speed=1500ms^-1
now, we need to calculate the wavelength of the pulse using the relation:
speed=f x wavelength
wavelength=speed/f=1500/6000=0.25m
converting it to cm=0.25x100=25.0cm
Hope this helps!

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Ohhh I totally forgot that it travels twice due to the reflection!

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