Answer:
The time required to receive the echo at the transducer is 
Explanation:
Frequency of ultrasonic beam, f = 5 MHz
It reflects off an object 5 cm deep.
We need to find the time required to receive the echo at the transducer. The ultrasonic wave is an electromagnetic wave. it moves with a speed of light. Let t is the time taken by the wave to go once.
So,



Time to receive the echo at the transducer gets doubled. So,

Hence, this is the required solution.
-1<v-2/21 = -19>v I think is the answer
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