Answer:
Option A
Explanation:
Mechanical waves requires some medium to travel through. They travel faster in the dense medium as compared to a free medium. 
The speed of a mechanical wave is fastest in the solid medium and the slowest in the gaseous medium. Hence, as the wave traverses from gaseous medium to the solid medium, its speed increases. 
Thus, option A is correct
 
        
             
        
        
        
Buhrs atomic model differed from ruthofords because it explained that electrons exist in specified energy levels surrounding the nucleus. This means that, Ruthoford believed that electrons can't do very much. However, Buhrs' model showed that electrons are much more powerful than anyone else believes they can be.
 
        
                    
             
        
        
        
Answer with Explanation:
We are given that 
A.Mass,m=12 kg


Speed,v=1.5m/s
Net force in x direction must be zero



Net force in y direction 








Power,P=Fv

Where 
B.Substitute the values 


 
        
             
        
        
        
Answer:
A. 50 m/s
Explanation:
Given in the y direction:
v₀ = 0 m/s
a = 10 m/s²
t = 4 s
Find: v
v = at + v₀
v = (10 m/s²) (4 s) + 0 m/s
v = 40 m/s
In the x direction, the velocity is constant at 30 m/s.
The overall speed is:
v² = (30 m/s)² + (40 m/s)²
v = 50 m/s
 
        
                    
             
        
        
        
B. The velocity of the second flight is negative compared to the speed.