The echo is heard 2.80 s later, this means this is the time the sound takes to travel to the reflecting object and then back to us. So, during this time, the sound wave has covered the distance L between us and the object twice:

The speed of the sound wave is:

, and since it is moving by uniform motion, we can find the distance covered by the wave using

And we said this corresponds to twice the distance between us and the reflecting object, so:

so, the object is 480 meters away.
Answer:
The voltage is 
Explanation:
From the question we are told that
The duty cycle is p = 65% = 0.65
The on - state voltage is 
Generally the average DC voltage is mathematically represented as

=> 
=> 
<span>diminution in the density of something, especially air or a gas.</span>
Non metals produce something called protons they are ions