Answer:
Because chemical energy is being converted into thermal energy.
Explanation:
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: 2 cm
Explanation:
Given , for a converging lens
Focal length : 
Height of object : 
Object distabce from lens : 
Using lens formula:
, we get
, where v = image distance from the lens.
On solving aboive equation , we get

Formula of Magnification :
, where h' is the height of image.
Put value of u, v and h in it , we get

Hence, the height of the image is 2 cm.
NO
The likelihood of reaching 40 miles per hour is very slim. Several factors are related to how quickly somebody can run, which is why only one person has ever run 28 miles per hour.Catch a sprinter smashing a speed record and they look like they could keep up with a car chase. 40 MPH: The fastest speed humans can run. The current fastest human in the world is Usain Bolt, who can run at nearly 28 miles per hour.Steve in Davis, Calif. So far, the fastest anyone has run is about 27½ miles per hour, a speed reached (briefly) by sprinter Usain Bolt just after the midpoint of his world-record 100-meter dash in 2009.
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