The density of air reduces as humidity and amount of water in the air increases. <span> The speed of sound is inversely proportional to the root of density, therefore sound travels faster on a cloudy day than on a dry day so, velocity of sound increase.</span>
Answer:The frequency of the echo is slightly decreased
Explanation:
Given
speed of boat 
cliff is 
away
when boat is still , suppose t is the time taken by the echo to reach observer on the boat
But as soon as boat starts moving the distance between cliff and boat decreasing and time for echo to reach observer also decreases
and we know 
therefore frequency of the echo slightly decreased.
It moves closer or farther to the protons and neutrons. Hope this helps.
The rock is kicked horizontally off the cliff at 20 m/s.
There's no air resistance, and gravity has no effect on horizontal motion. There's no horizontal force acting on the rock to make it move horizontally slower or faster than 20 m/s, so it keeps moving horizontally at 20 m/s.
It's in the air for 7 seconds before it hits the ground. Moving horizontally at 20 m/s for 7 seconds, it sails (20 x 7) = 140 meters horizontally away from the cliff.
