Where is the frequency of ultrasound in relation to the range of human ability to hear

The frequency of "ultra"sound is much much much higher than any frequency that any human being can hear.

Ultrasound frequencies in diagnostic radiology range from 2 MHz to approximately 15 MHz (although even higher frequencies may be used in some situations) !  That's a range from 100 times to 750 times the average limit of human hearing (20,000 Hz) !  (See more numbers below.)

Even when ultrasound blasts through your canal, shakes your tympanum, oscillates your ossicles, and attacks your hair cells, your brain never has a clue.

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Looking at it another way:

-- The exact upper and lower limits of human hearing are different for just about every individual on Earth.  As a broad average for the whole human race, we commonly consider the range to be from 20 Hz to 20,000 Hz .

That's a range of almost exactly 10 octaves.

-- Ultrasound operating at 2 MHz is another 6.6 octaves above the upper audible frequency limit.

--  Ultrasound operating at 15 MHz is another 9.5 octaves above the upper audible frequency limit.  

what was the acceleration of the 2 kg cart?

⇒ 16.0 cm/s2

what was the acceleration of the 4 kg cart?

⇒ 8.1 cm/s2

what was the acceleration of the 6 kg cart?

⇒ 5.3 cm/s2

connect the batteries in series and hope