Solar cells and solar panels are both integral, and closely related, parts of a solar energy system. When reading about solar energy systems, it may seem as if these titles are almost interchangeable. Writers refer to them both when discussing energy production and output, and often do so without explanation of how these parts work. However, each plays a distinct role. Solar cells contain all the parts necessary to convert sunlight to electricity. Solar panels combine and direct all of that energy output.
 
        
             
        
        
        
Answer:When the length of a string is changed, it will vibrate with a different frequency.Shorter strings have higher frequency and therefore higher pitch.
 
        
             
        
        
        
Answer:
this may be wrong but I am not sure
 
        
             
        
        
        
Sound pressure decreases with distance, so there's less sound pressure acting on your ear-drum. 
        
             
        
        
        
Answer:
Change in momentum is 1.1275 kg-m/s
Explanation:
It is given that,
Mass of the ball, m = 274 g = 0.274 kg
It hits the floor and rebounds upwards.
The ball hits the floor with a speed of 2.40 m/s i.e. u = -2.40 m/s  (-ve because the ball hits the ground)
It rebounds with a speed of 1.7 m/s i.e. v = 1.7 m/s (+ve because the ball rebounds in upward direction)
We have to find the change in the ball's momentum. It is given by :




So, the change in the momentum is 1.1275 kg-m/s