Answer A is incorrect
A crest is just one point. It is not the distance between 2 crests.
B  is incorrect
A trough is just 1 point. It is not the distance between 2 troughs.
C is incorrect.
the amplitude measures the height of a crest from the middle of the wave to the crest (or trough).
D is the correct answer. That is the distance between 2 crests or 2 troughs 
        
             
        
        
        
Answer:
a)
b)
c) 0 J/K
d)S= 61.53 J/K
Explanation:
Given that
T₁ = 745 K
T₂ = 101 K
Q= 7190 J
a)
The entropy change of reservoir 745 K

Negative sign because heat is leaving.

b)
The entropy change of reservoir 101 K


c)
The entropy change of the rod will be zero.
d)
The entropy change of the system 
S= S₁ + S₂ 
S = 71.18 - 9.65 J/K
S= 61.53 J/K
 
        
             
        
        
        
Answer:
2.06 m/s
Explanation:
From the law of conservation of linear momentum, the sum of momentum before and after collision are equal. Considering this case where we have frictionless surface, no momentum is lost in the process.
Momentum before collision
Momentum is given by p=mv where m and v represent mass. The initial sum of momentum will be 9v+(27*0.5)=9v+13.5
Momentum after collision
The momentum after collision will be given by (9+27)*0.9=32.4
Relating the two then 9v+13.5=32.4
9v=18.5
V=2.055555555555555555555555555555555555555 m/s
Rounded off, v is approximately 2.06 m/s
 
        
             
        
        
        
The elastic potential energy of the spring is 0.31 J
Explanation:
The elastic potential energy of a spring is given by

where
k is the spring constant
x is the compression/stretching of the spring
For the spring in this problem, we have:
k = 500 N/m (spring constant)
x = 0.035 m (compression)
Substituting, we find the elastic potential energy:

Learn more about potential energy:
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