The one word you're looking for to fill in the blank 
can be "uneven" or "non-uniform".
        
                    
             
        
        
        
I think its 13...........
        
             
        
        
        
The only vertical forces are weight and normal force, and they balance since the surface is horizontal. The horizontal forces are the applied force (uppercase F) in the direction the block slides and the frictional force (lowercase f) in the opposite direction.
Apply Newton's 2nd Law in the horizontal direction:
ΣF = ma
F - f = ma
where f = µmg
F - µmg = ma
F = m(a +µg)
F = (20 kg)(1.4 m/s² + 0.28(9.8 m/s²)
F = 83 N
        
             
        
        
        
Answer:
doppler effect
Explanation:
When the relative motion of two bodies results in the wavelength becoming shorter this means that the bodies are getting closer. This is known as blue shift.
When the relative motion of two bodies results in the wavelength becoming longer this means that the bodies are getting farther. This is known as red shift.
Collectively this phenomenon is known as the Doppler effect.
 
        
             
        
        
        
A parallel circuit exists when an electric charge flows in more than one path best describes it.
<h3>What is a Parallel circuit?</h3>
This type of circuit has branches in which the current divides and only part of it flows through any of the branch.
Parallel circuit having more than one branch therefore means that electric charge will flow in more than one path thereby making option A the most appropriate choice.
Read more about Parallel circuit here brainly.com/question/12069231